2022-10-31 05:59:52

by Gaosheng Cui

Subject: [PATCH] ext4: fix undefined behavior in bit shift for ext4_check_flag_values

Shifting signed 32-bit value by 31 bits is undefined, so changing
significant bit to unsigned. The UBSAN warning calltrace like below:

UBSAN: shift-out-of-bounds in fs/ext4/ext4.h:591:2
left shift of 1 by 31 places cannot be represented in type 'int'
Call Trace:
<TASK>
dump_stack_lvl+0x7d/0xa5
dump_stack+0x15/0x1b
ubsan_epilogue+0xe/0x4e
__ubsan_handle_shift_out_of_bounds+0x1e7/0x20c
ext4_init_fs+0x5a/0x277
do_one_initcall+0x76/0x430
kernel_init_freeable+0x3b3/0x422
kernel_init+0x24/0x1e0
ret_from_fork+0x1f/0x30
</TASK>

Fixes: 9a4c80194713 ("ext4: ensure Inode flags consistency are checked at build time")
Signed-off-by: Gaosheng Cui <[email protected]>
---
fs/ext4/ext4.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 8d5453852f98..e2d12e6c998d 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -558,7 +558,7 @@ enum {
*
* It's not paranoia if the Murphy's Law really *is* out to get you. :-)
*/
-#define TEST_FLAG_VALUE(FLAG) (EXT4_##FLAG##_FL == (1 << EXT4_INODE_##FLAG))
+#define TEST_FLAG_VALUE(FLAG) (EXT4_##FLAG##_FL == (1U << EXT4_INODE_##FLAG))
#define CHECK_FLAG_VALUE(FLAG) BUILD_BUG_ON(!TEST_FLAG_VALUE(FLAG))

static inline void ext4_check_flag_values(void)
--
2.25.1

2022-12-06 21:06:19

by Theodore Ts'o

Subject: Re: [PATCH] ext4: fix undefined behavior in bit shift for ext4_check_flag_values

On Mon, 31 Oct 2022 13:58:33 +0800, Gaosheng Cui wrote:
> Shifting signed 32-bit value by 31 bits is undefined, so changing
> significant bit to unsigned. The UBSAN warning calltrace like below:
>
> UBSAN: shift-out-of-bounds in fs/ext4/ext4.h:591:2
> left shift of 1 by 31 places cannot be represented in type 'int'
> Call Trace:
> <TASK>
> dump_stack_lvl+0x7d/0xa5
> dump_stack+0x15/0x1b
> ubsan_epilogue+0xe/0x4e
> __ubsan_handle_shift_out_of_bounds+0x1e7/0x20c
> ext4_init_fs+0x5a/0x277
> do_one_initcall+0x76/0x430
> kernel_init_freeable+0x3b3/0x422
> kernel_init+0x24/0x1e0
> ret_from_fork+0x1f/0x30
> </TASK>
>
> [...]

Applied, thanks!

[1/1] ext4: fix undefined behavior in bit shift for ext4_check_flag_values
commit: 0cd464d06ba0b9941dd285042909dc4d94adb373

Best regards,
--
Theodore Ts'o <[email protected]>