6.12-stable review patch. If anyone has any objections, please let me know.
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From: Gao Xiang hsiangkao@linux.alibaba.com
[ Upstream commit d53cd891f0e4311889349fff3a784dc552f814b9 ]
Otherwise, it could cause potential kernel stack overflow (e.g., EROFS mounting itself).
Reviewed-by: Sheng Yong shengyong1@xiaomi.com Fixes: fb176750266a ("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 Signed-off-by: Sasha Levin sashal@kernel.org --- fs/erofs/super.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)
diff --git a/fs/erofs/super.c b/fs/erofs/super.c index 5fcdab6145176..027fd567a4d9f 100644 --- a/fs/erofs/super.c +++ b/fs/erofs/super.c @@ -636,6 +636,22 @@ 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"); + return -ENOTBLK; + } + } sb->s_blocksize = PAGE_SIZE; sb->s_blocksize_bits = PAGE_SHIFT;