[PATCH 5.15 881/917] mm, thp: fix incorrect unmap behavior for private pages

Greg Kroah-Hartman
2021-11-16T00:39:12Z

From: Rongwei Wang <rongwei.wang@linux.alibaba.com>

commit 8468e937df1f31411d1e127fa38db064af051fe5 upstream.

When truncating pagecache on file THP, the private pages of a process
should not be unmapped mapping. This incorrect behavior on a dynamic
shared libraries which will cause related processes to happen core dump.

A simple test for a DSO (Prerequisite is the DSO mapped in file THP):

int main(int argc, char *argv[])
{
int fd;

fd = open(argv[1], O_WRONLY);
if (fd < 0) {
perror("open");
}

close(fd);
return 0;
}

The test only to open a target DSO, and do nothing. But this operation
will lead one or more process to happen core dump. This patch mainly to
fix this bug.

Link: https://lkml.kernel.org/r/20211025092134.18562-3-rongwei.wang@linux.alibaba.com
Fixes: eb6ecbed0aa2 ("mm, thp: relax the VM_DENYWRITE constraint on file-backed THPs")
Signed-off-by: Rongwei Wang <rongwei.wang@linux.alibaba.com>
Tested-by: Xu Yu <xuyu@linux.alibaba.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Song Liu <song@kernel.org>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Collin Fijalkovich <cfijalkovich@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/open.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

--- a/fs/open.c
+++ b/fs/open.c
@@ -857,8 +857,17 @@ static int do_dentry_open(struct file *f
*/
smp_mb();
if (filemap_nr_thps(inode->i_mapping)) {
+ struct address_space *mapping = inode->i_mapping;
+
filemap_invalidate_lock(inode->i_mapping);
- truncate_pagecache(inode, 0);
+ /*
+ * unmap_mapping_range just need to be called once
+ * here, because the private pages is not need to be
+ * unmapped mapping (e.g. data segment of dynamic
+ * shared libraries here).
+ */
+ unmap_mapping_range(mapping, 0, 0, 0);
+ truncate_inode_pages(mapping, 0);
filemap_invalidate_unlock(inode->i_mapping);
}
}