On 2025/11/24 10:03, Hongbo Li wrote:
Hi Xiang,
On 2025/11/22 14:23, Gao Xiang wrote:
Otherwise, it could cause potential kernel stack overflow (e.g., EROFS
mounting itself).
Reviewed-by: Sheng Yong <[email protected]>
Fixes: fb176750266a ("erofs: add file-backed mount support")
Signed-off-by: Gao Xiang <[email protected]>
---
Change since v1:
- Return -ENOTBLK instead of -EINVAL since userspace tools like
util-linux will fall back to using loop to mount again.
Don't use -ELOOP compared to other stacked fses, since -ENOTBLK is
more suitable: it means the kernel can't handle it anymore.
fs/erofs/super.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index f3f8d8c066e4..2db534f76464 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -639,6 +639,22 @@ static int erofs_fc_fill_super(struct super_block *sb,
struct fs_context *fc)
sbi->blkszbits = PAGE_SHIFT;
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");
Since it will success once the max stack depth is exceeded, a warning would be
better? Otherwise it looks good me.
But that is not a kernel fallback, and the kernel mount already fails,
I think erroring out is more proper.
Thanks,
Gao Xiang
Reviewed-by: Hongbo Li <[email protected]>
Thanks,
Hongbo
+ return -ENOTBLK;
+ }
+ }
sb->s_blocksize = PAGE_SIZE;
sb->s_blocksize_bits = PAGE_SHIFT;
