[PATCH] afs: Fix memory leak when mounting with multiple source parameters

[David Howells <dhowells@xxxxxxxxxx>]

There's a memory leak in afs_parse_source() whereby multiple source=
parameters overwrite fc->source in the fs_context struct without freeing
the previously recorded source.

Fix this by only permitting a single source parameter and rejecting with an
error all subsequent ones.

This was caught by syzbot with the kernel memory leak detector, showing
something like the following trace:

unreferenced object 0xffff888114375440 (size 32):
  comm "repro", pid 5168, jiffies 4294923723 (age 569.948s)
  hex dump (first 32 bytes):
    25 5e 5d 24 5b 2b 25 5d 28 24 7b 3a 0f 6b 5b 29  %^]$[+%](${:.k[)
    2d 3a 00 00 00 00 00 00 00 00 00 00 00 00 00 00  -:..............
  backtrace:
    [<0000000072e41e46>] slab_post_alloc_hook+0x42/0x79
    [<00000000d8b306e6>] __kmalloc_track_caller+0x125/0x16a
    [<0000000028ae1813>] kmemdup_nul+0x24/0x3c
    [<0000000072927516>] vfs_parse_fs_string+0x5a/0xa1
    [<0000000045b4b196>] generic_parse_monolithic+0x9d/0xc5
    [<0000000084462c80>] do_new_mount+0x10d/0x15a
    [<000000008aef98c5>] do_mount+0x5f/0x8e
    [<000000002998d632>] __do_sys_mount+0xff/0x127
    [<00000000faf86d94>] do_syscall_64+0x2d/0x3a
    [<000000004495c173>] entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: 13fcc6837049 ("afs: Add fs_context support")
Reported-by: syzbot+86dc6632faaca40133ab@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
---

 fs/afs/super.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/afs/super.c b/fs/afs/super.c
index 6c5900df6aa5..e38bb1e7a4d2 100644
--- a/fs/afs/super.c
+++ b/fs/afs/super.c
@@ -230,6 +230,9 @@ static int afs_parse_source(struct fs_context *fc, struct fs_parameter *param)
 
 	_enter(",%s", name);
 
+	if (fc->source)
+		return invalf(fc, "kAFS: Multiple sources not supported");
+
 	if (!name) {
 		printk(KERN_ERR "kAFS: no volume name specified\n");
 		return -EINVAL;