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exfat: fix shift-out-of-bounds in exfat_fill_super() 

syzbot reported a warning which could cause shift-out-of-bounds issue.

Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x183/0x22e lib/dump_stack.c:120
 ubsan_epilogue lib/ubsan.c:148 [inline]
 __ubsan_handle_shift_out_of_bounds+0x432/0x4d0 lib/ubsan.c:395
 exfat_read_boot_sector fs/exfat/super.c:471 [inline]
 __exfat_fill_super fs/exfat/super.c:556 [inline]
 exfat_fill_super+0x2acb/0x2d00 fs/exfat/super.c:624
 get_tree_bdev+0x406/0x630 fs/super.c:1291
 vfs_get_tree+0x86/0x270 fs/super.c:1496
 do_new_mount fs/namespace.c:2881 [inline]
 path_mount+0x1937/0x2c50 fs/namespace.c:3211
 do_mount fs/namespace.c:3224 [inline]
 __do_sys_mount fs/namespace.c:3432 [inline]
 __se_sys_mount+0x2f9/0x3b0 fs/namespace.c:3409
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

exfat specification describe sect_per_clus_bits field of boot sector
could be at most 25 - sect_size_bits and at least 0. And sect_size_bits
can also affect this calculation, It also needs validation.
This patch add validation for sect_per_clus_bits and sect_size_bits
field of boot sector.

Fixes: 719c1e1829 ("exfat: add super block operations")
Cc: stable@vger.kernel.org # v5.9+
Reported-by: syzbot+da4fe66aaadd3c2e2d1c@syzkaller.appspotmail.com
Reviewed-by: Sungjong Seo <sj1557.seo@samsung.com>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
This commit is contained in:
Namjae Jeon 2021-02-01 09:23:37 +09:00
parent f40ddce885
commit 78c276f549
2 changed files with 30 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
fs/exfat/exfat_raw.h
View File

@ -77,6 +77,10 @@
#define EXFAT_FILE_NAME_LEN 15
#define EXFAT_MIN_SECT_SIZE_BITS 9
#define EXFAT_MAX_SECT_SIZE_BITS 12
#define EXFAT_MAX_SECT_PER_CLUS_BITS(x) (25 - (x)->sect_size_bits)
/* EXFAT: Main and Backup Boot Sector (512 bytes) */
struct boot_sector {
__u8 jmp_boot[BOOTSEC_JUMP_BOOT_LEN];

31
fs/exfat/super.c
View File

@ -381,8 +381,7 @@ static int exfat_calibrate_blocksize(struct super_block *sb, int logical_sect)
{
struct exfat_sb_info *sbi = EXFAT_SB(sb);
if (!is_power_of_2(logical_sect) ||
logical_sect < 512 || logical_sect > 4096) {
if (!is_power_of_2(logical_sect)) {
exfat_err(sb, "bogus logical sector size %u", logical_sect);
return -EIO;
}
@ -451,6 +450,25 @@ static int exfat_read_boot_sector(struct super_block *sb)
return -EINVAL;
}
/*
* sect_size_bits could be at least 9 and at most 12.
*/
if (p_boot->sect_size_bits < EXFAT_MIN_SECT_SIZE_BITS ||
p_boot->sect_size_bits > EXFAT_MAX_SECT_SIZE_BITS) {
exfat_err(sb, "bogus sector size bits : %u\n",
p_boot->sect_size_bits);
return -EINVAL;
}
/*
* sect_per_clus_bits could be at least 0 and at most 25 - sect_size_bits.
*/
if (p_boot->sect_per_clus_bits > EXFAT_MAX_SECT_PER_CLUS_BITS(p_boot)) {
exfat_err(sb, "bogus sectors bits per cluster : %u\n",
p_boot->sect_per_clus_bits);
return -EINVAL;
}
sbi->sect_per_clus = 1 << p_boot->sect_per_clus_bits;
sbi->sect_per_clus_bits = p_boot->sect_per_clus_bits;
sbi->cluster_size_bits = p_boot->sect_per_clus_bits +
@ -477,16 +495,19 @@ static int exfat_read_boot_sector(struct super_block *sb)
sbi->used_clusters = EXFAT_CLUSTERS_UNTRACKED;
/* check consistencies */
if (sbi->num_FAT_sectors << p_boot->sect_size_bits <
sbi->num_clusters * 4) {
if ((u64)sbi->num_FAT_sectors << p_boot->sect_size_bits <
(u64)sbi->num_clusters * 4) {
exfat_err(sb, "bogus fat length");
return -EINVAL;
}
if (sbi->data_start_sector <
sbi->FAT1_start_sector + sbi->num_FAT_sectors * p_boot->num_fats) {
(u64)sbi->FAT1_start_sector +
(u64)sbi->num_FAT_sectors * p_boot->num_fats) {
exfat_err(sb, "bogus data start sector");
return -EINVAL;
}
if (sbi->vol_flags & VOLUME_DIRTY)
exfat_warn(sb, "Volume was not properly unmounted. Some data may be corrupt. Please run fsck.");
if (sbi->vol_flags & MEDIA_FAILURE)