Re: [patch] Btrfs: dereferencing free'd memory in panic message

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On 06/22/2012 09:30 AM, Dan Carpenter wrote:
On Fri, Jun 22, 2012 at 09:09:04AM -0400, Josef Bacik wrote:
On 06/22/2012 03:14 AM, Dan Carpenter wrote:
We free "node" and then dereference it in the panic message on the next
line.  I considered moving the kfree() after the panic given that panic
can return under certain configurations, but in the end I decided it
doesn't matter if we leak a bit after a panic.

Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
index 790f492..c50d80a 100644
--- a/fs/btrfs/relocation.c
+++ b/fs/btrfs/relocation.c
@@ -1239,7 +1239,6 @@ static int __must_check __add_reloc_root(struct btrfs_root *root)
  			      node->bytenr, &node->rb_node);
  	spin_unlock(&rc->reloc_root_tree.lock);
  	if (rb_node) {
-		kfree(node);
  		btrfs_panic(root->fs_info, -EEXIST, "Duplicate root found "
  			    "for start=%llu while inserting into relocation "
  			    "tree\n", node->bytenr);

Except btrfs_panic can not panic the box if it's mounted to not
panic on errors, so we still need to do the kfree afterwards.
Thanks,

Right.  I mentioned that in my change log, but I figured a one time
memory leak was the least of our concerns in that case.  I will
resend.  This should probably return -EEXIST here as well yes?


Ah sorry I thought you were talking about BUG_ON() not actually stopping the box in some cases. But yes I'd like to not leak anyway and return -EEXIST. Thanks,

Josef
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