| Message ID | 20241228115446.2478706-5-mjt@tls.msk.ru |
|---|---|
| State | Accepted |
| Commit | 0cb3ff7c22671aa1e1e227318799ccf6762c3bea |
| Headers | show |
| Series | [PULL,01/11] docs/devel: remove dead video link for sourcehut submit process | expand |
> Found with test sbsaref introduced in [1]. > > [1] https://patchew.org/QEMU/20241203213629.2482806-1-pierrick.bouvier@linaro.org/ > > ../block/vvfat.c:433:24: runtime error: index 14 out of bounds for type 'uint8_t [11]' > #0 0x56151a66b93a in create_long_filename ../block/vvfat.c:433 > #1 0x56151a66f3d7 in create_short_and_long_name ../block/vvfat.c:725 > #2 0x56151a670403 in read_directory ../block/vvfat.c:804 > #3 0x56151a674432 in init_directories ../block/vvfat.c:964 > #4 0x56151a67867b in vvfat_open ../block/vvfat.c:1258 > #5 0x56151a3b8e19 in bdrv_open_driver ../block.c:1660 > #6 0x56151a3bb666 in bdrv_open_common ../block.c:1985 > #7 0x56151a3cadb9 in bdrv_open_inherit ../block.c:4153 > #8 0x56151a3c8850 in bdrv_open_child_bs ../block.c:3731 > #9 0x56151a3ca832 in bdrv_open_inherit ../block.c:4098 > #10 0x56151a3cbe40 in bdrv_open ../block.c:4248 > #11 0x56151a46344f in blk_new_open ../block/block-backend.c:457 > #12 0x56151a388bd9 in blockdev_init ../blockdev.c:612 > #13 0x56151a38ab2d in drive_new ../blockdev.c:1006 > #14 0x5615190fca41 in drive_init_func ../system/vl.c:649 > #15 0x56151aa796dd in qemu_opts_foreach ../util/qemu-option.c:1135 > #16 0x5615190fd2b6 in configure_blockdev ../system/vl.c:708 > #17 0x56151910a307 in qemu_create_early_backends ../system/vl.c:2004 > #18 0x561519113fcf in qemu_init ../system/vl.c:3685 > #19 0x56151a7e438e in main ../system/main.c:47 > #20 0x7f72d1a46249 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58 > #21 0x7f72d1a46304 in __libc_start_main_impl ../csu/libc-start.c:360 > #22 0x561517e98510 in _start (/home/user/.work/qemu/build/qemu-system-aarch64+0x3b9b510) > > The offset used can easily go beyond entry->name size. It's probably a > bug, but I don't have the time to dive into vfat specifics for now. Hi Pierrick, Michael, this patch breaks the creation of long filenames in the vvfat driver. > This change solves the ubsan issue, and is functionally equivalent, as > anything written past the entry->name array would not be read anyway. This assumption is wrong. The guest reads the bytes written past the entry->name array in the 32 byte direntry_t structure. A LFN direntry structure is different from a regular direntry structure. You patch limits the long file name to 5 UCS-2 characters out of possible 13 UCS-2 characters per LFN entry. To reproduce the issue: On the host: ~> mkdir vvfat-drive ~> touch "vvfat-drive/file with a long name.txt" and start QEMU with -blockdev driver=vvfat,read-only=true,dir=./vvfat-drive,node-name=disk-d,label=hostdrive -device scsi-hd,bus=scsi0.0,scsi-id=0,lun=1,drive=disk-d On the guest without this patch: ~ # mount -t vfat -o ro /dev/sdb1 /mnt ~ # ls /mnt file with a long name.txt On the guest with this patch: ~ # mount -t vfat -o ro /dev/sdb1 /mnt ~ # ls /mnt file ~ # ls /mnt | xxd 00000000: 6669 6c65 200a file . With best regards, Volker > > Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org> > Reviewed-by: Michael Tokarev <mjt@tls.msk.ru> > Signed-off-by: Michael Tokarev <mjt@tls.msk.ru> > --- > block/vvfat.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/block/vvfat.c b/block/vvfat.c > index 8ffe8b3b9b..f2eafaa923 100644 > --- a/block/vvfat.c > +++ b/block/vvfat.c > @@ -426,6 +426,10 @@ static direntry_t *create_long_filename(BDRVVVFATState *s, const char *filename) > else if(offset<22) offset=14+offset-10; > else offset=28+offset-22; > entry=array_get(&(s->directory),s->directory.next-1-(i/26)); > + /* ensure we don't write anything past entry->name */ > + if (offset >= sizeof(entry->name)) { > + continue; > + } > if (i >= 2 * length + 2) { > entry->name[offset] = 0xff; > } else if (i % 2 == 0) {
diff --git a/block/vvfat.c b/block/vvfat.c index 8ffe8b3b9b..f2eafaa923 100644 --- a/block/vvfat.c +++ b/block/vvfat.c @@ -426,6 +426,10 @@ static direntry_t *create_long_filename(BDRVVVFATState *s, const char *filename) else if(offset<22) offset=14+offset-10; else offset=28+offset-22; entry=array_get(&(s->directory),s->directory.next-1-(i/26)); + /* ensure we don't write anything past entry->name */ + if (offset >= sizeof(entry->name)) { + continue; + } if (i >= 2 * length + 2) { entry->name[offset] = 0xff; } else if (i % 2 == 0) {