[PATCH] module: always complete idempotent loads

[Vegard Nossum]

Commit 9b9879fc0327 added a hashtable storing lists of concurrent module
loads. However, it didn't fix up all the error paths in
init_module_from_file(); this would lead to leaving the function while an
on-stack 'struct idempotent' element is still in the hash table, which
leads to all sorts of badness as spotted by syzkaller:

    BUG: soft lockup in sys_finit_module
    BUG: unable to handle kernel paging request in init_module_from_file
    general protection fault in init_module_from_file
    INFO: task hung in init_module_from_file
    KASAN: out-of-bounds Read in init_module_from_file
    KASAN: slab-out-of-bounds Read in init_module_from_file
    KASAN: slab-use-after-free Read in init_module_from_file
    KASAN: slab-use-after-free Read in set_powered_sync
    KASAN: stack-out-of-bounds Read in init_module_from_file
    KASAN: use-after-free in init_module_from_file
    KASAN: use-after-free Read in init_module_from_file

Fixes: 9b9879fc0327 ("modules: catch concurrent module loads, treat them as idempotent")
Reported-by: Harshit Mogalapalli <harshit.m.mogalapalli@xxxxxxxxxx>
Reported-by: syzbot+9c2bdc9d24e4a7abe741@xxxxxxxxxxxxxxxxxxxxxxxxx
Tested-by: Harshit Mogalapalli <harshit.m.mogalapalli@xxxxxxxxxx>
Cc: Johan Hovold <johan@xxxxxxxxxx>
Cc: Johan Hovold <johan@xxxxxxxxxx>
Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Rudi Heitbaum <rudi@xxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
---
 kernel/module/main.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/module/main.c b/kernel/module/main.c
index d6de66a6a1ac..6100d0373f2f 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -3121,39 +3121,42 @@ static void idempotent_complete(struct idempotent *u, int ret)
 static int init_module_from_file(struct file *f, const char __user * uargs, int flags)
 {
 	struct idempotent idem;
 	struct load_info info = { };
 	void *buf = NULL;
 	int len, ret;
 
 	if (!f || !(f->f_mode & FMODE_READ))
 		return -EBADF;
 
 	if (idempotent(&idem, file_inode(f))) {
 		wait_for_completion(&idem.complete);
 		return idem.ret;
 	}
 
 	len = kernel_read_file(f, 0, &buf, INT_MAX, NULL, READING_MODULE);
 	if (len < 0) {
 		mod_stat_inc(&failed_kreads);
 		mod_stat_add_long(len, &invalid_kread_bytes);
-		return len;
+		ret = len;
+		goto out;
 	}
 
 	if (flags & MODULE_INIT_COMPRESSED_FILE) {
 		int err = module_decompress(&info, buf, len);
 		vfree(buf); /* compressed data is no longer needed */
 		if (err) {
 			mod_stat_inc(&failed_decompress);
 			mod_stat_add_long(len, &invalid_decompress_bytes);
-			return err;
+			ret = err;
+			goto out;
 		}
 	} else {
 		info.hdr = buf;
 		info.len = len;
 	}
 
 	ret = load_module(&info, uargs, flags);
+out:
 	idempotent_complete(&idem, ret);
 	return ret;
 }
--