[RFAv2] Fix buffer overflow regression due to minsym malloc-ed instead of obstack-ed.
Philippe Waroquiers
philippe.waroquiers@skynet.be
Sun Mar 24 09:19:00 GMT 2019
Note: this is version 2. The first RFA (RFQ) was not examining the last
element of the array, as the stop condition in the loop must be <=
instead of <.
Valgrind detects the following error in a bunch of tests,
e.g. in gdb.base/foll-fork.exp.
==15155== VALGRIND_GDB_ERROR_BEGIN
==15155== Invalid read of size 8
==15155== at 0x55BE04: minimal_symbol_upper_bound(bound_minimal_symbol) (minsyms.c:1504)
==15155== by 0x3B2E9C: find_pc_partial_function(unsigned long, char const**, unsigned long*, unsigned long*, block const**) (blockframe.c:340)
==15155== by 0x3B3135: find_function_entry_range_from_pc(unsigned long, char const**, unsigned long*, unsigned long*) (blockframe.c:385)
==15155== by 0x4F5597: fill_in_stop_func(gdbarch*, execution_control_state*) [clone .part.16] (infrun.c:4124)
==15155== by 0x4FBE01: fill_in_stop_func (infrun.c:7636)
==15155== by 0x4FBE01: process_event_stop_test(execution_control_state*) (infrun.c:6279)
...
==15155== Address 0x715bec8 is 0 bytes after a block of size 2,952 alloc'd
==15155== at 0x4C2E2B3: realloc (vg_replace_malloc.c:836)
==15155== by 0x405F2C: xrealloc (common-utils.c:62)
==15155== by 0x55BA4E: xresizevec<minimal_symbol> (poison.h:170)
==15155== by 0x55BA4E: minimal_symbol_reader::install() (minsyms.c:1399)
==15155== by 0x4981C7: elf_read_minimal_symbols (elfread.c:1165)
...
This seems to be a regression created by:
commit 042d75e42c5572f333e0e06dabd3c5c4afab486c
Author: Tom Tromey <tom@tromey.com>
AuthorDate: Sat Mar 2 12:29:48 2019 -0700
Commit: Tom Tromey <tom@tromey.com>
CommitDate: Fri Mar 15 16:02:10 2019 -0600
Allocate minimal symbols with malloc
Before this commit, the array of 'struct minimal_symbol'
contained a last element that was a "null symbol". The comment in
minimal_symbol_reader::install was:
/* We also terminate the minimal symbol table with a "null symbol",
which is *not* included in the size of the table. This makes it
easier to find the end of the table when we are handed a pointer
to some symbol in the middle of it. Zero out the fields in the
"null symbol" allocated at the end of the array. Note that the
symbol count does *not* include this null symbol, which is why it
is indexed by mcount and not mcount-1. */
memset (&msymbols[mcount], 0, sizeof (struct minimal_symbol));
However, minimal_symbol_upper_bound was still based on the assumption
that the array of minsym is terminated by a minsym with a null symbol:
it is looping with:
for (i = 1; MSYMBOL_LINKAGE_NAME (msymbol + i) != NULL; i++)
Replace this NULL comparison by a logic that calculates how
many msymbol are following the msymbols from which we are starting from.
(Re-)tested on debian/amd64, natively and under valgrind.
Note that a bunch of comments in minimal_symbol_reader::install
are still referring to allocations being done in obstack. These
comments seem obsolete. I have not fixed them, as I have not
understood what they are explaining (e.g. related to language
auto, demangling, etc : I have not seen where all this is done).
gdb/ChangeLog
2019-03-24 Philippe Waroquiers <philippe.waroquiers@skynet.be>
* minsyms.c (minimal_symbol_upper_bound): Fix buffer overflow
by computing the nr of symbols after msymbol.
---
gdb/minsyms.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/gdb/minsyms.c b/gdb/minsyms.c
index b95e9ef6e8..3db21d1309 100644
--- a/gdb/minsyms.c
+++ b/gdb/minsyms.c
@@ -1501,7 +1501,10 @@ minimal_symbol_upper_bound (struct bound_minimal_symbol minsym)
msymbol = minsym.minsym;
section = MSYMBOL_SECTION (msymbol);
- for (i = 1; MSYMBOL_LINKAGE_NAME (msymbol + i) != NULL; i++)
+ int n_after_msymbol = minsym.objfile->per_bfd->minimal_symbol_count
+ - (msymbol - minsym.objfile->per_bfd->msymbols.get ())
+ - 1;
+ for (i = 1; i <= n_after_msymbol; i++)
{
if ((MSYMBOL_VALUE_RAW_ADDRESS (msymbol + i)
!= MSYMBOL_VALUE_RAW_ADDRESS (msymbol))
@@ -1510,7 +1513,7 @@ minimal_symbol_upper_bound (struct bound_minimal_symbol minsym)
}
obj_section = MSYMBOL_OBJ_SECTION (minsym.objfile, minsym.minsym);
- if (MSYMBOL_LINKAGE_NAME (msymbol + i) != NULL
+ if (i <= n_after_msymbol
&& (MSYMBOL_VALUE_ADDRESS (minsym.objfile, msymbol + i)
< obj_section_endaddr (obj_section)))
result = MSYMBOL_VALUE_ADDRESS (minsym.objfile, msymbol + i);
--
2.20.1
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