[PATCH mm-hotfixes-stable] procfs: fix possible double mmput() in do_procmap_query()

[Andrii Nakryiko <andrii@kernel.org>]

When user provides incorrectly sized buffer for build ID for PROCMAP_QUERY we
return with -ENAMETOOLONG error. After recent changes this condition happens
later, after we unlocked mmap_lock/per-VMA lock and did mmput(), so original
goto out is now wrong and will double-mmput() mm_struct. Fix by jumping
further to clean up only vm_file and name_buf.

Fixes: b5cbacd7f86f ("procfs: avoid fetching build ID while holding VMA lock")
Reported-by: Ruikai Peng <ruikai@pwno.io>
Reported-by: Thomas Gleixner <tglx@kernel.org>
Reported-by: syzbot+237b5b985b78c1da9600@syzkaller.appspotmail.com
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 fs/proc/task_mmu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 26188a4ad1ab..2f55efc36816 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -780,7 +780,7 @@ static int do_procmap_query(struct mm_struct *mm, void __user *uarg)
 		} 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 +808,7 @@ static int do_procmap_query(struct mm_struct *mm, void __user *uarg)
 out:
 	query_vma_teardown(&lock_ctx);
 	mmput(mm);
+out_file:
 	if (vm_file)
 		fput(vm_file);
 	kfree(name_buf);
-- 
2.47.3