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author | Mark Wielaard <mark@klomp.org> | 2022-07-28 15:31:12 +0200 |
---|---|---|
committer | Ryan Goldberg <rgoldber@redhat.com> | 2022-08-04 14:11:42 -0400 |
commit | 2f5e894a6f015aed3dbe7935ce06397e1f1e9976 (patch) | |
tree | aa44dbab1111aa636fbfd4397339462835c1b631 | |
parent | 8aa511b6cfeee5e8a5f8b93536323ca1fafd2509 (diff) | |
download | elfutils-2f5e894a6f015aed3dbe7935ce06397e1f1e9976.tar.gz |
libdwfl: Rewrite reading of ar_size in elf_begin_rand
With GCC 12.1.1, glibc 2.35, -fsanitize=undefined and
-D_FORTIFY_SOURCE=3 we get the following error message:
In file included from /usr/include/ar.h:22,
from ../libelf/libelfP.h:33,
from core-file.c:31:
In function ‘pread’,
inlined from ‘pread_retry’ at ../lib/system.h:188:21,
inlined from ‘elf_begin_rand’ at core-file.c:86:16,
inlined from ‘core_file_read_eagerly’ at core-file.c:205:15:
/usr/include/bits/unistd.h:74:10: error: ‘__pread_alias’ writing 58 or more bytes into a region of size 10 overflows the destination [-Werror=stringop-overflow=]
74 | return __glibc_fortify (pread, __nbytes, sizeof (char),
| ^~~~~~~~~~~~~~~
/usr/include/ar.h: In function ‘core_file_read_eagerly’:
/usr/include/ar.h:41:10: note: destination object ‘ar_size’ of size 10
41 | char ar_size[10]; /* File size, in ASCII decimal. */
| ^~~~~~~
/usr/include/bits/unistd.h:50:16: note: in a call to function ‘__pread_alias’ declared with attribute ‘access (write_only, 2, 3)’
50 | extern ssize_t __REDIRECT (__pread_alias,
| ^~~~~~~~~~
cc1: all warnings being treated as errors
The warning disappears when dropping either -fsanitize=undefined
or when using -D_FORTIFY_SOURCE=2. It looks like a false positive.
But I haven't figured out how/why it happens.
The code is a little tricky to proof correct though. The ar_size
field is a not-zero terminated string ASCII decimal, right-padded
with spaces. Which is then converted with strtoll. Relying on the
fact that the struct ar_hdr is zero initialized, so there will be
a zero byte after the ar_size field.
Rewrite the code to just use a zero byte terminated char array.
Which is much easier to reason about. As a bonus the error disappears.
Signed-off-by: Mark Wielaard <mark@klomp.org>
-rw-r--r-- | libdwfl/ChangeLog | 5 | ||||
-rw-r--r-- | libdwfl/core-file.c | 26 |
2 files changed, 21 insertions, 10 deletions
diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog index 75c53948..acdaa013 100644 --- a/libdwfl/ChangeLog +++ b/libdwfl/ChangeLog @@ -1,3 +1,8 @@ +2022-07-28 Mark Wielaard <mark@klomp.org> + + * core-file.c (elf_begin_rand): Replace struct ar_hdr h with + a char ar_size[AR_SIZE_CHARS + 1] array to read size. + 2022-07-18 Shahab Vahedi <shahab@synopsys.com> * debuginfod-client.c (dwfl_get_debuginfod_client stub): diff --git a/libdwfl/core-file.c b/libdwfl/core-file.c index cefc3db0..4418ef33 100644 --- a/libdwfl/core-file.c +++ b/libdwfl/core-file.c @@ -75,26 +75,32 @@ elf_begin_rand (Elf *parent, off_t offset, off_t size, off_t *next) from the archive header to override SIZE. */ if (parent->kind == ELF_K_AR) { - struct ar_hdr h = { .ar_size = "" }; - - if (unlikely (parent->maximum_size - offset < sizeof h)) + /* File size, in ASCII decimal, right-padded with ASCII spaces. + Max 10 characters. Not zero terminated. So make this ar_size + array one larger and explicitly zero terminate it. As needed + for strtoll. */ + #define AR_SIZE_CHARS 10 + char ar_size[AR_SIZE_CHARS + 1]; + ar_size[AR_SIZE_CHARS] = '\0'; + + if (unlikely (parent->maximum_size - offset < sizeof (struct ar_hdr))) return fail (ELF_E_RANGE); if (parent->map_address != NULL) - memcpy (h.ar_size, parent->map_address + parent->start_offset + offset, - sizeof h.ar_size); + memcpy (ar_size, parent->map_address + parent->start_offset + offset, + AR_SIZE_CHARS); else if (unlikely (pread_retry (parent->fildes, - h.ar_size, sizeof (h.ar_size), + ar_size, AR_SIZE_CHARS, parent->start_offset + offset + offsetof (struct ar_hdr, ar_size)) - != sizeof (h.ar_size))) + != AR_SIZE_CHARS)) return fail (ELF_E_READ_ERROR); - offset += sizeof h; + offset += sizeof (struct ar_hdr); char *endp; - size = strtoll (h.ar_size, &endp, 10); - if (unlikely (endp == h.ar_size) + size = strtoll (ar_size, &endp, 10); + if (unlikely (endp == ar_size) || unlikely ((off_t) parent->maximum_size - offset < size)) return fail (ELF_E_INVALID_ARCHIVE); } |