[PATCH] procfs: Prevent double mmput() in do_procmap_query()

[Thomas Gleixner <tglx@kernel.org>]

A recent fix moved the build ID evaluation past the mmput() of the success
path but kept the error goto unchanged, which ends up in doing another
quert_vma_teardown() and another mmput().

Change the goto so it jumps past the mmput() and only puts the file and
the buffer.

Fixes: b5cbacd7f86f ("procfs: avoid fetching build ID while holding VMA lock")
Reported-by: syzbot+237b5b985b78c1da9600@syzkaller.appspotmail.com
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Closes: https://lore.kernel.org/698aaf3c.050a0220.3b3015.0088.GAE@google.com/T/#u
---
 fs/proc/task_mmu.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -780,7 +780,7 @@ static int do_procmap_query(struct mm_st
 		} else {
 			if (karg.build_id_size < build_id_sz) {
 				err = -ENAMETOOLONG;
-				goto out;
+				goto out_file;
 			}
 			karg.build_id_size = build_id_sz;
 		}
@@ -808,6 +808,8 @@ static int do_procmap_query(struct mm_st
 out:
 	query_vma_teardown(&lock_ctx);
 	mmput(mm);
+
+out_file:
 	if (vm_file)
 		fput(vm_file);
 	kfree(name_buf);