On 4/2/22 06:06, Vitaly Chikunov wrote:
`struct dirent' returned from readdir(3) could be shorter (or longer)
than `sizeof(struct dirent)', thus memcpy of sizeof length will overread
into unallocated page causing SIGSEGV. Example stack trace:
#0 0x00005555559ebeed v9fs_co_readdir_many (/usr/bin/qemu-system-x86_64 +
0x497eed)
#1 0x00005555559ec2e9 v9fs_readdir (/usr/bin/qemu-system-x86_64 + 0x4982e9)
#2 0x0000555555eb7983 coroutine_trampoline (/usr/bin/qemu-system-x86_64 +
0x963983)
#3 0x00007ffff73e0be0 n/a (n/a + 0x0)
While fixing, provide a helper for any future `struct dirent' cloning.
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/841
Cc: qemu-sta...@nongnu.org
Co-authored-by: Christian Schoenebeck <qemu_...@crudebyte.com>
Signed-off-by: Vitaly Chikunov <v...@altlinux.org>
---
Tested on x86-64 Linux again.
Changes from v2:
- Make it work with a simulated dirent where d_reclen is 0, which was
caused abort in readdir qos-test, by using fallback at runtime.
hw/9pfs/codir.c | 3 +--
include/qemu/osdep.h | 13 +++++++++++++
util/osdep.c | 18 ++++++++++++++++++
3 files changed, 32 insertions(+), 2 deletions(-)
+struct dirent *
+qemu_dirent_dup(struct dirent *dent)
+{
+ size_t sz = 0;
+#if defined _DIRENT_HAVE_D_RECLEN
+ /* Avoid use of strlen() if there's d_reclen. */
+ sz = dent->d_reclen;
+#endif
+ if (sz == 0) {
If _DIRENT_HAVE_D_RECLEN is defined, this case is unlikely...
+ /* Fallback to the most portable way. */
+ sz = offsetof(struct dirent, d_name) +
+ strlen(dent->d_name) + 1;
+ }
+ struct dirent *dst = g_malloc(sz);
+ return memcpy(dst, dent, sz);
+}
What about this?
struct dirent *
qemu_dirent_dup(struct dirent *dent)
{
size_t sz;
#if defined _DIRENT_HAVE_D_RECLEN
/* Avoid use of strlen() if there's d_reclen. */
sz = dent->d_reclen;
#else
/* Fallback to the most portable way. */
sz = offsetof(struct dirent, d_name) +
strlen(dent->d_name) + 1;
#endif
return g_memdup(dent, sz);
}
