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erofs: limit the level of fs stacking for file-backed mounts 

Otherwise, it could cause potential kernel stack overflow (e.g., EROFS
mounting itself).

Reviewed-by: Sheng Yong <shengyong1@xiaomi.com>
Fixes: fb17675026 ("erofs: add file-backed mount support")
Reviewed-by: Chao Yu <chao@kernel.org>
Reviewed-by: Hongbo Li <lihongbo22@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
This commit is contained in:
Gao Xiang 2025-11-22 14:23:32 +08:00
parent ebe4f3f6eb
commit d53cd891f0
1 changed files with 16 additions and 0 deletions
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16
fs/erofs/super.c
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@ -639,6 +639,22 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
sbi->blkszbits = PAGE_SHIFT; sbi->blkszbits = PAGE_SHIFT;
if (!sb->s_bdev) { if (!sb->s_bdev) {
/*
* (File-backed mounts) EROFS claims it's safe to nest other
* fs contexts (including its own) due to self-controlled RO
* accesses/contexts and no side-effect changes that need to
* context save & restore so it can reuse the current thread
* context. However, it still needs to bump `s_stack_depth` to
* avoid kernel stack overflow from nested filesystems.
*/
if (erofs_is_fileio_mode(sbi)) {
sb->s_stack_depth =
file_inode(sbi->dif0.file)->i_sb->s_stack_depth + 1;
if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
erofs_err(sb, "maximum fs stacking depth exceeded");
return -ENOTBLK;
}
}
sb->s_blocksize = PAGE_SIZE; sb->s_blocksize = PAGE_SIZE;
sb->s_blocksize_bits = PAGE_SHIFT; sb->s_blocksize_bits = PAGE_SHIFT;