[PATCH AUTOSEL 4.19 3/4] btrfs: send: limit number of clones and allocated memory size

[Sasha Levin <sashal@kernel.org>]

From: David Sterba <dsterba@suse.com>

[ Upstream commit 33e17b3f5ab74af12aca58c515bc8424ff69a343 ]

The arg->clone_sources_count is u64 and can trigger a warning when a
huge value is passed from user space and a huge array is allocated.
Limit the allocated memory to 8MiB (can be increased if needed), which
in turn limits the number of clone sources to 8M / sizeof(struct
clone_root) = 8M / 40 = 209715.  Real world number of clones is from
tens to hundreds, so this is future proof.

Reported-by: syzbot+4376a9a073770c173269@syzkaller.appspotmail.com
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/btrfs/send.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index 80d248e88761d..1f535cd990d3c 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -6826,10 +6826,10 @@ long btrfs_ioctl_send(struct file *mnt_file, struct btrfs_ioctl_send_args *arg)
 	/*
 	 * Check that we don't overflow at later allocations, we request
 	 * clone_sources_count + 1 items, and compare to unsigned long inside
-	 * access_ok.
+	 * access_ok. Also set an upper limit for allocation size so this can't
+	 * easily exhaust memory. Max number of clone sources is about 200K.
 	 */
-	if (arg->clone_sources_count >
-	    ULONG_MAX / sizeof(struct clone_root) - 1) {
+	if (arg->clone_sources_count > SZ_8M / sizeof(struct clone_root)) {
 		ret = -EINVAL;
 		goto out;
 	}
-- 
2.39.0