romfs_lookup() and romfs_readdir() walk a directory's entry chain by following ri.next, and stop only once the offset is zero or past the end of the image. Nothing stops an entry from pointing at itself, so on a crafted image a lookup of a name that is not present spins forever. That loop has no cond_resched() and no signal check, so the task cannot be killed, and it spins with i_rwsem held and the dentry left in the in-lookup state. A second lookup of the same name then waits forever in d_alloc_parallel(), and it is that waiter the hung task watchdog reports, which makes this look like a dcache problem: INFO: task syz-executor239:5636 blocked for more than 143 seconds. d_alloc_parallel+0xd13/0x16c0 fs/dcache.c:2839 __lookup_slow+0x82/0x2f0 fs/namei.c:1904 Require the chain to move forward and return -EIO if it does not. File headers are laid out in increasing order and both loops already treat the chain as a bounded forward-only walk, so this only enforces what they assume. In romfs_readdir() a cycle never advances ctx->pos and has getdents() repeat entries forever, so check there too. The hard link chain bounded by commit d30b5a954e0a ("romfs: detect hard link cycles") is a separate one. Sangho Lee posted a fix for this chain in July 2026 that validates it at inode instantiation; it has had no replies. Reported-by: syzbot+e8ebfecec06a009dd2d3@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=e8ebfecec06a009dd2d3 Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Palla Raghunath --- fs/romfs/super.c | 26 +++++++++++++++++++++----- 1 file changed, 21 insertions(+), 5 deletions(-) diff --git a/fs/romfs/super.c b/fs/romfs/super.c index 7f783d6173e8..846b57f265ef 100644 --- a/fs/romfs/super.c +++ b/fs/romfs/super.c @@ -143,7 +143,7 @@ static int romfs_readdir(struct file *file, struct dir_context *ctx) { struct inode *i = file_inode(file); struct romfs_inode ri; - unsigned long offset, maxoff; + unsigned long offset, maxoff, next; int j, ino, nextfh; char fsname[ROMFS_MAXFN]; /* XXX dynamic? */ int ret; @@ -191,7 +191,16 @@ static int romfs_readdir(struct file *file, struct dir_context *ctx) romfs_dtype_table[nextfh & ROMFH_TYPE])) goto out; - offset = nextfh & ROMFH_MASK; + /* likewise, a chain that does not move forward would have + * getdents() repeat entries forever + */ + next = nextfh & ROMFH_MASK; + if (next && next <= offset) { + offset = maxoff; + ctx->pos = offset; + goto out; + } + offset = next; } out: return 0; @@ -203,7 +212,7 @@ static int romfs_readdir(struct file *file, struct dir_context *ctx) static struct dentry *romfs_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags) { - unsigned long offset, maxoff; + unsigned long offset, maxoff, next; struct inode *inode = NULL; struct romfs_inode ri; const char *name; /* got from dentry */ @@ -245,8 +254,15 @@ static struct dentry *romfs_lookup(struct inode *dir, struct dentry *dentry, break; } - /* next entry */ - offset = be32_to_cpu(ri.next) & ROMFH_MASK; + /* next entry; the chain must move forward, or a corrupt image + * will keep us here forever + */ + next = be32_to_cpu(ri.next) & ROMFH_MASK; + if (next && next <= offset) { + ret = -EIO; + goto error; + } + offset = next; } return d_splice_alias(inode, dentry); -- 2.34.1