On 2022/11/1 15:33, Baokun Li wrote:
When squashfs_read_table() returns an error or `sb->s_magic
!= SQUASHFS_MAGIC`, enters the error branch and calls
msblk->thread_ops->destroy(msblk) to destroy msblk.
However, msblk->thread_ops has not been initialized.
Therefore, the following problem is triggered:
==================================================================
BUG: KASAN: null-ptr-deref in squashfs_fill_super+0xe7a/0x13b0
Read of size 8 at addr 0000000000000008 by task swapper/0/1
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.1.0-rc3-next-20221031 #367
Call Trace:
<TASK>
dump_stack_lvl+0x73/0x9f
print_report+0x743/0x759
kasan_report+0xc0/0x120
__asan_load8+0xd3/0x140
squashfs_fill_super+0xe7a/0x13b0
get_tree_bdev+0x27b/0x450
squashfs_get_tree+0x19/0x30
vfs_get_tree+0x49/0x150
path_mount+0xaae/0x1350
init_mount+0xad/0x100
do_mount_root+0xbc/0x1d0
mount_block_root+0x173/0x316
mount_root+0x223/0x236
prepare_namespace+0x1eb/0x237
kernel_init_freeable+0x528/0x576
kernel_init+0x29/0x250
ret_from_fork+0x1f/0x30
</TASK>
==================================================================
To solve this issue, msblk->thread_ops is initialized immediately after
msblk is assigned a value.
Fixes: b0645770d3c7 ("squashfs: add the mount parameter theads=<single|multi|percpu>")
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
---
Thank you for helping to identify and fix this bug.
Reviewed-by: Xiaoming Ni <nixiaoming@xxxxxxxxxx>
fs/squashfs/super.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/squashfs/super.c b/fs/squashfs/super.c
index 1e428ca9414e..7d5265a39d20 100644
--- a/fs/squashfs/super.c
+++ b/fs/squashfs/super.c
@@ -197,6 +197,7 @@ static int squashfs_fill_super(struct super_block *sb, struct fs_context *fc)
return -ENOMEM;
}
msblk = sb->s_fs_info;
+ msblk->thread_ops = opts->thread_ops;
msblk->panic_on_errors = (opts->errors == Opt_errors_panic);
@@ -231,7 +232,7 @@ static int squashfs_fill_super(struct super_block *sb, struct fs_context *fc)
sb->s_bdev);
goto failed_mount;
}
- msblk->thread_ops = opts->thread_ops;
+
if (opts->thread_num == 0) {
msblk->max_thread_num = msblk->thread_ops->max_decompressors();
} else {
