On 2022-07-28 09:48, Mark Wielaard wrote:
With GCC 12.1.1, glibc 2.3a, -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.
Interesting, I'll take a closer look at this from the gcc context. I
obviously don't have any strong opinions about the elfutils patch :)
Thanks,
Sid
The code is a little tricky to proof correct though. The ar_size
field is a not-zero terminated string ASCII decimal, right-paddedr
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 <m...@klomp.org>
---
libdwfl/ChangeLog | 5 +++++
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 <m...@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 <sha...@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);
}
