Summary: | incorrect match in multi-byte (non-UTF8) string | ||
---|---|---|---|
Product: | glibc | Reporter: | Leonardo Chiquitto <leonardo> |
Component: | regex | Assignee: | Ulrich Drepper <drepper.fsp> |
Status: | RESOLVED FIXED | ||
Severity: | normal | CC: | fweimer, sbrabec |
Priority: | P2 | Flags: | fweimer:
security-
|
Version: | 2.15 | ||
Target Milestone: | --- | ||
Host: | Target: | ||
Build: | Last reconfirmed: | ||
Attachments: |
reg.sh: a script to reproduce the problem
glibc-regex-incomplete-char.patch glibc-regex-incomplete-char.patch glibc-regex-incomplete-char.patch |
Created attachment 6207 [details]
glibc-regex-incomplete-char.patch
Proposed fix. There is another bug in sed that triggers infinite loop.
Description:
re_search_internal() inside switch(match_kind) in case 6 finds a possible match. In case of our false match, verification of match not respecting multi-byte characters fails and match_regex() returns index of such false match.
Going deeper, re_search_internal() calls re_string_reconstruct() and that calls re_string_skip_chars().
re_string_skip_chars() is a I18N specific function that jumps by characters up to the indexed character. It is a multi-byte character wise function.
In case of correct run, it returns correct index to the next character to inspect. In case of bug occurrence, __mbrtowc called from there returns -2 (incomplete multi-byte character). Why? It seems to be caused by remain_len being equal 1, even if there is still 6 bytes to inspect ("\267\357a\277\267\275").
I believe, that remain_len is computed incorrectly:
sed-4.2.1/lib/regex_internal.c:502 re_string_skip_chars()
remain_len = pstr->len - rawbuf_idx;
pstr->len seems to be length of the remaining part of the string, rawbuf_idx is the index of the remaining part of the string in the original (raw) string.
I am not quite familiar with the code, but I believe that the expression should be:
remain_len = pstr->raw_len - rawbuf_idx;
Example:
stop in the first iteration of the re_string_skip_chars()
Correct case (two leading "a" characters):
rawbuf_idx = 5
*pstr = {
raw_mbs = 0x6479b0 "aa\267\357a\277\267\275", <incomplete sequence \350>, mbs
= 0x6479b2 "\267\357a\277\267\275", <incomplete sequence \350>,
wcs = 0x648190, offsets = 0x0, cur_state = {__count = 0, __value = {
__wch = 0, __wchb = "\000\000\000"}}, raw_mbs_idx = 2,
valid_len = 0, valid_raw_len = 3, bufs_len = 4, cur_idx = 2,
raw_len = 9, len = 7, raw_stop = 9, stop = 7, tip_context = 0,
trans = 0x0, word_char = 0x647d88, icase = 0 '\000',
is_utf8 = 0 '\000', map_notascii = 0 '\000', mbs_allocated = 0 '\000',
offsets_needed = 0 '\000', newline_anchor = 0 '\000',
word_ops_used = 0 '\000', mb_cur_max = 3}
Buggy case (three leading "a" characters):
rawbuf_idx = 6
*pstr = {
raw_mbs = 0x6479b0 "aaa\267\357a\277\267\275", <incomplete sequence \350>,
mbs = 0x6479b3 "\267\357a\277\267\275", <incomplete sequence \350>,
wcs = 0x648190, offsets = 0x0, cur_state = {__count = 0, __value = {
__wch = 0, __wchb = "\000\000\000"}}, raw_mbs_idx = 3,
valid_len = 0, valid_raw_len = 3, bufs_len = 4, cur_idx = 2,
raw_len = 10, len = 7, raw_stop = 10, stop = 7, tip_context = 0,
trans = 0x0, word_char = 0x647d88, icase = 0 '\000',
is_utf8 = 0 '\000', map_notascii = 0 '\000', mbs_allocated = 0 '\000',
offsets_needed = 0 '\000', newline_anchor = 0 '\000',
word_ops_used = 0 '\000', mb_cur_max = 3}
If my observation is correct, the bug is not EUC-JP specific.
Bug triggers:
- Charset must be capable to constitute false match on the boundary of two characters. EUC-JP fits this requirement, UTF-8 probably does not.
- There is a true ASCII match that is false match in locale specific charset.
- This false match must appear in an exact place near two thirds of the string.
Cross references: libc-alpha mailing list: http://sourceware.org/ml/libc-alpha/2012-02/msg00206.html http://sourceware.org/ml/libc-alpha/2012-02/msg00267.html sed+grep: sed: http://lists.gnu.org/archive/html/bug-gnu-utils/2012-02/msg00016.html sed testcase: http://lists.gnu.org/archive/html/bug-gnu-utils/2012-02/msg00017.html grep: http://lists.gnu.org/archive/html/bug-gnu-utils/2012-02/msg00018.html Created attachment 6244 [details]
glibc-regex-incomplete-char.patch
New patch with fixed ChangeLog entry and testcase.
Created attachment 6252 [details] glibc-regex-incomplete-char.patch Updated patch. Changes since comment 3: - Testcase uses test-skeleton.c. - Uses SBC_MAX and includes "regex_internal.h". - Setup fastmap before call to re_compile_pattern. - bug-regex33.6 comment updated: There is one true and one false match. |
Created attachment 6186 [details] reg.sh: a script to reproduce the problem When a special string composed of single and multi-byte characters is passed to re_search(), the function seems to lose track of which characters are multi-byte and returns an incorrect match. This seems to be exclusive to the ja_JP.eucjp locale. The problem can be reproduced when the following string: aaa\xb7\xefa\xbf\xb7\xbd\xe8 ... is matched against the pattern: \xb7\xbd The two bytes in the pattern are respectively "the last byte of the second multi-byte char" and "the first byte of the third multi-byte char" in the original string. The number of "a"s prefixed in the original string seems to make all the difference here. I could only reproduce the problem when exactly 3 or 4 "a"s are prefixed. I.e., if you remove one "a" from the prefix of the original string: aa\xb7\xefa\xbf\xb7\xbd\xe8 ... the problem no longer happens. I'm attaching a script that reproduces the problem. The 'sed' version I'm using is compiled with "--without-included-regex", so it should use glibc's regex functions. Unfortunately I can't affirm yet that the bug is not in sed, but I'm trying to create a self contained program to demonstrate the problem.