The following test segfaults on a 64-bit system (haven't tested 32-bit). (Any precision less than 0x7fffffe0 is OK; 0x7fffffe0 through 0x7fffffff result in the crash.) #include <stdio.h> #include <stdlib.h> int main (void) { FILE *fp; if ((fp = fopen ("/dev/null", "w")) == NULL) exit (1); fprintf (fp, "%2$.*1$a", 0x7fffffff, 1e200); } The problem is the code in printf_positional: /* Maybe the buffer is too small. */ if (MAX (prec, width) + EXTSIZ > WORK_BUFFER_SIZE) { if (__libc_use_alloca ((MAX (prec, width) + EXTSIZ) * sizeof (CHAR_T))) workend = ((CHAR_T *) alloca ((MAX (prec, width) + EXTSIZ) * sizeof (CHAR_T)) + (MAX (prec, width) + EXTSIZ)); else { workstart = (CHAR_T *) malloc ((MAX (prec, width) + EXTSIZ) * sizeof (CHAR_T)); if (workstart == NULL) { done = -1; goto all_done; } workend = workstart + (MAX (prec, width) + EXTSIZ); } } The code in the implementation that doesn't use '$' argument numbers has a check if (__glibc_unlikely (width >= INT_MAX / sizeof (CHAR_T) - EXTSIZ)) { __set_errno (EOVERFLOW); done = -1; goto all_done; } (and likewise for precision). The implementation for the case with '$' argument numbers is missing that check. So MAX (prec, width) + EXTSIZ overflows.
The master branch has been updated by Joseph Myers <jsm28@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=6caddd34bd7ffb5ac4f36c8e036eee100c2cc535 commit 6caddd34bd7ffb5ac4f36c8e036eee100c2cc535 Author: Joseph Myers <joseph@codesourcery.com> Date: Tue Jul 7 14:54:12 2020 +0000 Remove most vfprintf width/precision-dependent allocations (bug 14231, bug 26211). The vfprintf implementation (used for all printf-family functions) contains complicated logic to allocate internal buffers of a size depending on the width and precision used for a format, using either malloc or alloca depending on that size, and with consequent checks for size overflow and allocation failure. As noted in bug 26211, the version of that logic used when '$' plus argument number formats are in use is missing the overflow checks, which can result in segfaults (quite possibly exploitable, I didn't try to work that out) when the width or precision is in the range 0x7fffffe0 through 0x7fffffff (maybe smaller values as well in the wprintf case on 32-bit systems, when the multiplication by sizeof (CHAR_T) can overflow). All that complicated logic in fact appears to be useless. As far as I can tell, there has been no need (outside the floating-point printf code, which does its own allocations) for allocations depending on width or precision since commit 3e95f6602b226e0de06aaff686dc47b282d7cc16 ("Remove limitation on size of precision for integers", Sun Sep 12 21:23:32 1999 +0000). Thus, this patch removes that logic completely, thereby fixing both problems with excessive allocations for large width and precision for non-floating-point formats, and the problem with missing overflow checks with such allocations. Note that this does have the consequence that width and precision up to INT_MAX are now allowed where previously INT_MAX / sizeof (CHAR_T) - EXTSIZ or more would have been rejected, so could potentially expose any other overflows where the value would previously have been rejected by those removed checks. I believe this completely fixes bugs 14231 and 26211. Excessive allocations are still possible in the floating-point case (bug 21127), as are other integer or buffer overflows (see bug 26201). This does not address the cases where a precision larger than INT_MAX (embedded in the format string) would be meaningful without printf's return value overflowing (when it's used with a string format, or %g without the '#' flag, so the actual output will be much smaller), as mentioned in bug 17829 comment 8; using size_t internally for precision to handle that case would be complicated by struct printf_info being a public ABI. Nor does it address the matter of an INT_MIN width being negated (bug 17829 comment 7; the same logic appears a second time in the file as well, in the form of multiplying by -1). There may be other sources of memory allocations with malloc in printf functions as well (bug 24988, bug 16060). From inspection, I think there are also integer overflows in two copies of "if ((width -= len) < 0)" logic (where width is int, len is size_t and a very long string could result in spurious padding being output on a 32-bit system before printf overflows the count of output characters). Tested for x86-64 and x86.
Fixed for 2.32. commit 6caddd34bd7ffb5ac4f36c8e036eee100c2cc535 Author: Joseph Myers <joseph@codesourcery.com> Date: Tue Jul 7 14:54:12 2020 +0000 Remove most vfprintf width/precision-dependent allocations (bug 14231, bug 26211). The vfprintf implementation (used for all printf-family functions) contains complicated logic to allocate internal buffers of a size depending on the width and precision used for a format, using either malloc or alloca depending on that size, and with consequent checks for size overflow and allocation failure. As noted in bug 26211, the version of that logic used when '$' plus argument number formats are in use is missing the overflow checks, which can result in segfaults (quite possibly exploitable, I didn't try to work that out) when the width or precision is in the range 0x7fffffe0 through 0x7fffffff (maybe smaller values as well in the wprintf case on 32-bit systems, when the multiplication by sizeof (CHAR_T) can overflow). All that complicated logic in fact appears to be useless. As far as I can tell, there has been no need (outside the floating-point printf code, which does its own allocations) for allocations depending on width or precision since commit 3e95f6602b226e0de06aaff686dc47b282d7cc16 ("Remove limitation on size of precision for integers", Sun Sep 12 21:23:32 1999 +0000). Thus, this patch removes that logic completely, thereby fixing both problems with excessive allocations for large width and precision for non-floating-point formats, and the problem with missing overflow checks with such allocations. Note that this does have the consequence that width and precision up to INT_MAX are now allowed where previously INT_MAX / sizeof (CHAR_T) - EXTSIZ or more would have been rejected, so could potentially expose any other overflows where the value would previously have been rejected by those removed checks. I believe this completely fixes bugs 14231 and 26211. Excessive allocations are still possible in the floating-point case (bug 21127), as are other integer or buffer overflows (see bug 26201). This does not address the cases where a precision larger than INT_MAX (embedded in the format string) would be meaningful without printf's return value overflowing (when it's used with a string format, or %g without the '#' flag, so the actual output will be much smaller), as mentioned in bug 17829 comment 8; using size_t internally for precision to handle that case would be complicated by struct printf_info being a public ABI. Nor does it address the matter of an INT_MIN width being negated (bug 17829 comment 7; the same logic appears a second time in the file as well, in the form of multiplying by -1). There may be other sources of memory allocations with malloc in printf functions as well (bug 24988, bug 16060). From inspection, I think there are also integer overflows in two copies of "if ((width -= len) < 0)" logic (where width is int, len is size_t and a very long string could result in spurious padding being output on a 32-bit system before printf overflows the count of output characters). Tested for x86-64 and x86.
The master branch has been updated by Andreas Schwab <schwab@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=ca6466e8be32369a658035d69542d47603e58a99 commit ca6466e8be32369a658035d69542d47603e58a99 Author: Andreas Schwab <schwab@suse.de> Date: Mon Aug 29 15:05:40 2022 +0200 Add test for bug 29530 This tests for a bug that was introduced in commit edc1686af0 ("vfprintf: Reuse work_buffer in group_number") and fixed as a side effect of commit 6caddd34bd ("Remove most vfprintf width/precision-dependent allocations (bug 14231, bug 26211).").
The release/2.31/master branch has been updated by Florian Weimer <fw@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=1dbe841a672f5d6fdaf73c5d50774a2944a7d42b commit 1dbe841a672f5d6fdaf73c5d50774a2944a7d42b Author: Joseph Myers <joseph@codesourcery.com> Date: Tue Jul 7 14:54:12 2020 +0000 Remove most vfprintf width/precision-dependent allocations (bug 14231, bug 26211). The vfprintf implementation (used for all printf-family functions) contains complicated logic to allocate internal buffers of a size depending on the width and precision used for a format, using either malloc or alloca depending on that size, and with consequent checks for size overflow and allocation failure. As noted in bug 26211, the version of that logic used when '$' plus argument number formats are in use is missing the overflow checks, which can result in segfaults (quite possibly exploitable, I didn't try to work that out) when the width or precision is in the range 0x7fffffe0 through 0x7fffffff (maybe smaller values as well in the wprintf case on 32-bit systems, when the multiplication by sizeof (CHAR_T) can overflow). All that complicated logic in fact appears to be useless. As far as I can tell, there has been no need (outside the floating-point printf code, which does its own allocations) for allocations depending on width or precision since commit 3e95f6602b226e0de06aaff686dc47b282d7cc16 ("Remove limitation on size of precision for integers", Sun Sep 12 21:23:32 1999 +0000). Thus, this patch removes that logic completely, thereby fixing both problems with excessive allocations for large width and precision for non-floating-point formats, and the problem with missing overflow checks with such allocations. Note that this does have the consequence that width and precision up to INT_MAX are now allowed where previously INT_MAX / sizeof (CHAR_T) - EXTSIZ or more would have been rejected, so could potentially expose any other overflows where the value would previously have been rejected by those removed checks. I believe this completely fixes bugs 14231 and 26211. Excessive allocations are still possible in the floating-point case (bug 21127), as are other integer or buffer overflows (see bug 26201). This does not address the cases where a precision larger than INT_MAX (embedded in the format string) would be meaningful without printf's return value overflowing (when it's used with a string format, or %g without the '#' flag, so the actual output will be much smaller), as mentioned in bug 17829 comment 8; using size_t internally for precision to handle that case would be complicated by struct printf_info being a public ABI. Nor does it address the matter of an INT_MIN width being negated (bug 17829 comment 7; the same logic appears a second time in the file as well, in the form of multiplying by -1). There may be other sources of memory allocations with malloc in printf functions as well (bug 24988, bug 16060). From inspection, I think there are also integer overflows in two copies of "if ((width -= len) < 0)" logic (where width is int, len is size_t and a very long string could result in spurious padding being output on a 32-bit system before printf overflows the count of output characters). Tested for x86-64 and x86. (cherry picked from commit 6caddd34bd7ffb5ac4f36c8e036eee100c2cc535)
The release/2.30/master branch has been updated by Florian Weimer <fw@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=2c2357eedebcd93be932031f567c0c66c664131d commit 2c2357eedebcd93be932031f567c0c66c664131d Author: Joseph Myers <joseph@codesourcery.com> Date: Tue Jul 7 14:54:12 2020 +0000 Remove most vfprintf width/precision-dependent allocations (bug 14231, bug 26211). The vfprintf implementation (used for all printf-family functions) contains complicated logic to allocate internal buffers of a size depending on the width and precision used for a format, using either malloc or alloca depending on that size, and with consequent checks for size overflow and allocation failure. As noted in bug 26211, the version of that logic used when '$' plus argument number formats are in use is missing the overflow checks, which can result in segfaults (quite possibly exploitable, I didn't try to work that out) when the width or precision is in the range 0x7fffffe0 through 0x7fffffff (maybe smaller values as well in the wprintf case on 32-bit systems, when the multiplication by sizeof (CHAR_T) can overflow). All that complicated logic in fact appears to be useless. As far as I can tell, there has been no need (outside the floating-point printf code, which does its own allocations) for allocations depending on width or precision since commit 3e95f6602b226e0de06aaff686dc47b282d7cc16 ("Remove limitation on size of precision for integers", Sun Sep 12 21:23:32 1999 +0000). Thus, this patch removes that logic completely, thereby fixing both problems with excessive allocations for large width and precision for non-floating-point formats, and the problem with missing overflow checks with such allocations. Note that this does have the consequence that width and precision up to INT_MAX are now allowed where previously INT_MAX / sizeof (CHAR_T) - EXTSIZ or more would have been rejected, so could potentially expose any other overflows where the value would previously have been rejected by those removed checks. I believe this completely fixes bugs 14231 and 26211. Excessive allocations are still possible in the floating-point case (bug 21127), as are other integer or buffer overflows (see bug 26201). This does not address the cases where a precision larger than INT_MAX (embedded in the format string) would be meaningful without printf's return value overflowing (when it's used with a string format, or %g without the '#' flag, so the actual output will be much smaller), as mentioned in bug 17829 comment 8; using size_t internally for precision to handle that case would be complicated by struct printf_info being a public ABI. Nor does it address the matter of an INT_MIN width being negated (bug 17829 comment 7; the same logic appears a second time in the file as well, in the form of multiplying by -1). There may be other sources of memory allocations with malloc in printf functions as well (bug 24988, bug 16060). From inspection, I think there are also integer overflows in two copies of "if ((width -= len) < 0)" logic (where width is int, len is size_t and a very long string could result in spurious padding being output on a 32-bit system before printf overflows the count of output characters). Tested for x86-64 and x86. (cherry picked from commit 6caddd34bd7ffb5ac4f36c8e036eee100c2cc535)
The release/2.30/master branch has been updated by Florian Weimer <fw@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=d0aac8b4833c725d0682108066a210bbb7cf3bf4 commit d0aac8b4833c725d0682108066a210bbb7cf3bf4 Author: Andreas Schwab <schwab@suse.de> Date: Mon Aug 29 15:05:40 2022 +0200 Add test for bug 29530 This tests for a bug that was introduced in commit edc1686af0 ("vfprintf: Reuse work_buffer in group_number") and fixed as a side effect of commit 6caddd34bd ("Remove most vfprintf width/precision-dependent allocations (bug 14231, bug 26211)."). (cherry picked from commit ca6466e8be32369a658035d69542d47603e58a99)
The release/2.31/master branch has been updated by Florian Weimer <fw@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c8f2a3e8038232f7707d11b4629f5d5cf32244fc commit c8f2a3e8038232f7707d11b4629f5d5cf32244fc Author: Andreas Schwab <schwab@suse.de> Date: Mon Aug 29 15:05:40 2022 +0200 Add test for bug 29530 This tests for a bug that was introduced in commit edc1686af0 ("vfprintf: Reuse work_buffer in group_number") and fixed as a side effect of commit 6caddd34bd ("Remove most vfprintf width/precision-dependent allocations (bug 14231, bug 26211)."). (cherry picked from commit ca6466e8be32369a658035d69542d47603e58a99)
The release/2.29/master branch has been updated by Florian Weimer <fw@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=5b5dd5a43d0e13529a86332a5c10bdd5b5185e38 commit 5b5dd5a43d0e13529a86332a5c10bdd5b5185e38 Author: Joseph Myers <joseph@codesourcery.com> Date: Tue Jul 7 14:54:12 2020 +0000 Remove most vfprintf width/precision-dependent allocations (bug 14231, bug 26211). The vfprintf implementation (used for all printf-family functions) contains complicated logic to allocate internal buffers of a size depending on the width and precision used for a format, using either malloc or alloca depending on that size, and with consequent checks for size overflow and allocation failure. As noted in bug 26211, the version of that logic used when '$' plus argument number formats are in use is missing the overflow checks, which can result in segfaults (quite possibly exploitable, I didn't try to work that out) when the width or precision is in the range 0x7fffffe0 through 0x7fffffff (maybe smaller values as well in the wprintf case on 32-bit systems, when the multiplication by sizeof (CHAR_T) can overflow). All that complicated logic in fact appears to be useless. As far as I can tell, there has been no need (outside the floating-point printf code, which does its own allocations) for allocations depending on width or precision since commit 3e95f6602b226e0de06aaff686dc47b282d7cc16 ("Remove limitation on size of precision for integers", Sun Sep 12 21:23:32 1999 +0000). Thus, this patch removes that logic completely, thereby fixing both problems with excessive allocations for large width and precision for non-floating-point formats, and the problem with missing overflow checks with such allocations. Note that this does have the consequence that width and precision up to INT_MAX are now allowed where previously INT_MAX / sizeof (CHAR_T) - EXTSIZ or more would have been rejected, so could potentially expose any other overflows where the value would previously have been rejected by those removed checks. I believe this completely fixes bugs 14231 and 26211. Excessive allocations are still possible in the floating-point case (bug 21127), as are other integer or buffer overflows (see bug 26201). This does not address the cases where a precision larger than INT_MAX (embedded in the format string) would be meaningful without printf's return value overflowing (when it's used with a string format, or %g without the '#' flag, so the actual output will be much smaller), as mentioned in bug 17829 comment 8; using size_t internally for precision to handle that case would be complicated by struct printf_info being a public ABI. Nor does it address the matter of an INT_MIN width being negated (bug 17829 comment 7; the same logic appears a second time in the file as well, in the form of multiplying by -1). There may be other sources of memory allocations with malloc in printf functions as well (bug 24988, bug 16060). From inspection, I think there are also integer overflows in two copies of "if ((width -= len) < 0)" logic (where width is int, len is size_t and a very long string could result in spurious padding being output on a 32-bit system before printf overflows the count of output characters). Tested for x86-64 and x86. (cherry picked from commit 6caddd34bd7ffb5ac4f36c8e036eee100c2cc535)
The release/2.29/master branch has been updated by Florian Weimer <fw@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=6da40102c73018dd88bb959e460fa1425270d395 commit 6da40102c73018dd88bb959e460fa1425270d395 Author: Andreas Schwab <schwab@suse.de> Date: Mon Aug 29 15:05:40 2022 +0200 Add test for bug 29530 This tests for a bug that was introduced in commit edc1686af0 ("vfprintf: Reuse work_buffer in group_number") and fixed as a side effect of commit 6caddd34bd ("Remove most vfprintf width/precision-dependent allocations (bug 14231, bug 26211)."). (cherry picked from commit ca6466e8be32369a658035d69542d47603e58a99)
The release/2.28/master branch has been updated by Florian Weimer <fw@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=e1c0c00cc2bdd147bfcf362ada1443bee90465ec commit e1c0c00cc2bdd147bfcf362ada1443bee90465ec Author: Joseph Myers <joseph@codesourcery.com> Date: Tue Jul 7 14:54:12 2020 +0000 Remove most vfprintf width/precision-dependent allocations (bug 14231, bug 26211). The vfprintf implementation (used for all printf-family functions) contains complicated logic to allocate internal buffers of a size depending on the width and precision used for a format, using either malloc or alloca depending on that size, and with consequent checks for size overflow and allocation failure. As noted in bug 26211, the version of that logic used when '$' plus argument number formats are in use is missing the overflow checks, which can result in segfaults (quite possibly exploitable, I didn't try to work that out) when the width or precision is in the range 0x7fffffe0 through 0x7fffffff (maybe smaller values as well in the wprintf case on 32-bit systems, when the multiplication by sizeof (CHAR_T) can overflow). All that complicated logic in fact appears to be useless. As far as I can tell, there has been no need (outside the floating-point printf code, which does its own allocations) for allocations depending on width or precision since commit 3e95f6602b226e0de06aaff686dc47b282d7cc16 ("Remove limitation on size of precision for integers", Sun Sep 12 21:23:32 1999 +0000). Thus, this patch removes that logic completely, thereby fixing both problems with excessive allocations for large width and precision for non-floating-point formats, and the problem with missing overflow checks with such allocations. Note that this does have the consequence that width and precision up to INT_MAX are now allowed where previously INT_MAX / sizeof (CHAR_T) - EXTSIZ or more would have been rejected, so could potentially expose any other overflows where the value would previously have been rejected by those removed checks. I believe this completely fixes bugs 14231 and 26211. Excessive allocations are still possible in the floating-point case (bug 21127), as are other integer or buffer overflows (see bug 26201). This does not address the cases where a precision larger than INT_MAX (embedded in the format string) would be meaningful without printf's return value overflowing (when it's used with a string format, or %g without the '#' flag, so the actual output will be much smaller), as mentioned in bug 17829 comment 8; using size_t internally for precision to handle that case would be complicated by struct printf_info being a public ABI. Nor does it address the matter of an INT_MIN width being negated (bug 17829 comment 7; the same logic appears a second time in the file as well, in the form of multiplying by -1). There may be other sources of memory allocations with malloc in printf functions as well (bug 24988, bug 16060). From inspection, I think there are also integer overflows in two copies of "if ((width -= len) < 0)" logic (where width is int, len is size_t and a very long string could result in spurious padding being output on a 32-bit system before printf overflows the count of output characters). Tested for x86-64 and x86. (cherry picked from commit 6caddd34bd7ffb5ac4f36c8e036eee100c2cc535)
The release/2.28/master branch has been updated by Florian Weimer <fw@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=8b915921fbf4d32bf68fc3d637413cf96236b3fd commit 8b915921fbf4d32bf68fc3d637413cf96236b3fd Author: Andreas Schwab <schwab@suse.de> Date: Mon Aug 29 15:05:40 2022 +0200 Add test for bug 29530 This tests for a bug that was introduced in commit edc1686af0 ("vfprintf: Reuse work_buffer in group_number") and fixed as a side effect of commit 6caddd34bd ("Remove most vfprintf width/precision-dependent allocations (bug 14231, bug 26211)."). (cherry picked from commit ca6466e8be32369a658035d69542d47603e58a99)