[PATCH v5 1/5] vfat: fix missing sb_min_blocksize() return value checks

Yongpeng Yang
2025-11-03T16:48:02Z

From: Yongpeng Yang <yangyongpeng@xiaomi.com>

When emulating an nvme device on qemu with both logical_block_size and
physical_block_size set to 8 KiB, but without format, a kernel panic
was triggered during the early boot stage while attempting to mount a
vfat filesystem.

[95553.682035] EXT4-fs (nvme0n1): unable to set blocksize
[95553.684326] EXT4-fs (nvme0n1): unable to set blocksize
[95553.686501] EXT4-fs (nvme0n1): unable to set blocksize
[95553.696448] ISOFS: unsupported/invalid hardware sector size 8192
[95553.697117] ------------[ cut here ]------------
[95553.697567] kernel BUG at fs/buffer.c:1582!
[95553.697984] Oops: invalid opcode: 0000 [#1] SMP NOPTI
[95553.698602] CPU: 0 UID: 0 PID: 7212 Comm: mount Kdump: loaded Not tainted 6.18.0-rc2+ #38 PREEMPT(voluntary)
[95553.699511] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[95553.700534] RIP: 0010:folio_alloc_buffers+0x1bb/0x1c0
[95553.701018] Code: 48 8b 15 e8 93 18 02 65 48 89 35 e0 93 18 02 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f 5d 31 d2 31 c9 31 f6 31 ff c3 cc cc cc cc <0f> 0b 90 66 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f
[95553.702648] RSP: 0018:ffffd1b0c676f990 EFLAGS: 00010246
[95553.703132] RAX: ffff8cfc4176d820 RBX: 0000000000508c48 RCX: 0000000000000001
[95553.703805] RDX: 0000000000002000 RSI: 0000000000000000 RDI: 0000000000000000
[95553.704481] RBP: ffffd1b0c676f9c8 R08: 0000000000000000 R09: 0000000000000000
[95553.705148] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
[95553.705816] R13: 0000000000002000 R14: fffff8bc8257e800 R15: 0000000000000000
[95553.706483] FS: 000072ee77315840(0000) GS:ffff8cfdd2c8d000(0000) knlGS:0000000000000000
[95553.707248] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[95553.707782] CR2: 00007d8f2a9e5a20 CR3: 0000000039d0c006 CR4: 0000000000772ef0
[95553.708439] PKRU: 55555554
[95553.708734] Call Trace:
[95553.709015] <TASK>
[95553.709266] __getblk_slow+0xd2/0x230
[95553.709641] ? find_get_block_common+0x8b/0x530
[95553.710084] bdev_getblk+0x77/0xa0
[95553.710449] __bread_gfp+0x22/0x140
[95553.710810] fat_fill_super+0x23a/0xfc0
[95553.711216] ? __pfx_setup+0x10/0x10
[95553.711580] ? __pfx_vfat_fill_super+0x10/0x10
[95553.712014] vfat_fill_super+0x15/0x30
[95553.712401] get_tree_bdev_flags+0x141/0x1e0
[95553.712817] get_tree_bdev+0x10/0x20
[95553.713177] vfat_get_tree+0x15/0x20
[95553.713550] vfs_get_tree+0x2a/0x100
[95553.713910] vfs_cmd_create+0x62/0xf0
[95553.714273] __do_sys_fsconfig+0x4e7/0x660
[95553.714669] __x64_sys_fsconfig+0x20/0x40
[95553.715062] x64_sys_call+0x21ee/0x26a0
[95553.715453] do_syscall_64+0x80/0x670
[95553.715816] ? __fs_parse+0x65/0x1e0
[95553.716172] ? fat_parse_param+0x103/0x4b0
[95553.716587] ? vfs_parse_fs_param_source+0x21/0xa0
[95553.717034] ? __do_sys_fsconfig+0x3d9/0x660
[95553.717548] ? __x64_sys_fsconfig+0x20/0x40
[95553.717957] ? x64_sys_call+0x21ee/0x26a0
[95553.718360] ? do_syscall_64+0xb8/0x670
[95553.718734] ? __x64_sys_fsconfig+0x20/0x40
[95553.719141] ? x64_sys_call+0x21ee/0x26a0
[95553.719545] ? do_syscall_64+0xb8/0x670
[95553.719922] ? x64_sys_call+0x1405/0x26a0
[95553.720317] ? do_syscall_64+0xb8/0x670
[95553.720702] ? __x64_sys_close+0x3e/0x90
[95553.721080] ? x64_sys_call+0x1b5e/0x26a0
[95553.721478] ? do_syscall_64+0xb8/0x670
[95553.721841] ? irqentry_exit+0x43/0x50
[95553.722211] ? exc_page_fault+0x90/0x1b0
[95553.722681] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[95553.723166] RIP: 0033:0x72ee774f3afe
[95553.723562] Code: 73 01 c3 48 8b 0d 0a 33 0f 00 f7 d8 64 89 01 48 83 c8 ff c3 0f 1f 84 00 00 00 00 00 f3 0f 1e fa 49 89 ca b8 af 01 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d da 32 0f 00 f7 d8 64 89 01 48
[95553.725188] RSP: 002b:00007ffe97148978 EFLAGS: 00000246 ORIG_RAX: 00000000000001af
[95553.725892] RAX: ffffffffffffffda RBX: 00005dcfe53d0080 RCX: 000072ee774f3afe
[95553.726526] RDX: 0000000000000000 RSI: 0000000000000006 RDI: 0000000000000003
[95553.727176] RBP: 00007ffe97148ac0 R08: 0000000000000000 R09: 000072ee775e7ac0
[95553.727818] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
[95553.728459] R13: 00005dcfe53d04b0 R14: 000072ee77670b00 R15: 00005dcfe53d1a28
[95553.729086] </TASK>

The panic occurs as follows:
1. logical_block_size is 8KiB, causing {struct super_block *sb}->s_blocksize
is initialized to 0.
vfat_fill_super
- fat_fill_super
- sb_min_blocksize
- sb_set_blocksize //return 0 when size is 8KiB.
2. __bread_gfp is called with size == 0, causing folio_alloc_buffers() to
compute an offset equal to folio_size(folio), which triggers a BUG_ON.
fat_fill_super
- sb_bread
- __bread_gfp // size == {struct super_block *sb}->s_blocksize == 0
- bdev_getblk
- __getblk_slow
- grow_buffers
- grow_dev_folio
- folio_alloc_buffers // size == 0
- folio_set_bh //offset == folio_size(folio) and panic

To fix this issue, add proper return value checks for
sb_min_blocksize().

Cc: <stable@vger.kernel.org> # v6.15
Fixes: a64e5a596067bd ("bdev: add back PAGE_SIZE block size validation
for sb_set_blocksize()")
Reviewed-by: Matthew Wilcox <willy@infradead.org>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Yongpeng Yang <yangyongpeng@xiaomi.com>
---
v5:
- add cc tag for 5th patch
v4:
- split the changes into 5 patches
v3:
- remove the unnecessary blocksize variable definition
v2:
- add the __must_check mark to sb_min_blocksize() and include the Fixes
tag
---
fs/fat/inode.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 9648ed097816..9cfe20a3daaf 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -1595,8 +1595,12 @@ int fat_fill_super(struct super_block *sb, struct fs_context *fc,

setup(sb); /* flavour-specific stuff that needs options */

+ error = -EINVAL;
+ if (!sb_min_blocksize(sb, 512)) {
+ fat_msg(sb, KERN_ERR, "unable to set blocksize");
+ goto out_fail;
+ }
error = -EIO;
- sb_min_blocksize(sb, 512);
bh = sb_bread(sb, 0);
if (bh == NULL) {
fat_msg(sb, KERN_ERR, "unable to read boot sector");
--
2.43.0