[137/147] fs/coredump.c: log if a core dump is aborted due to changed file permissions

Commit Message

Andrew Morton Sept. 8, 2021, 3 a.m. UTC

From: David Oberhollenzer <[e-mail]>
Subject: fs/coredump.c: log if a core dump is aborted due to changed file permissions

For obvious security reasons, a core dump is aborted if the filesystem
cannot preserve ownership or permissions of the dump file.

This affects filesystems like e.g.  vfat, but also something like a 9pfs
share in a Qemu test setup, running as a regular user, depending on the
security model used.  In those cases, the result is an empty core file and
a confused user.

To hopefully safe other people a lot of time figuring out the cause, this
patch adds a simple log message for those specific cases.

[[e-mail]: s/|%s/%s/ in printk text]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: David Oberhollenzer <[e-mail]>
Cc: Al Viro <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 fs/coredump.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

Patch

--- a/fs/coredump.c~log-if-a-core-dump-is-aborted-due-to-changed-file-permissions
+++ a/fs/coredump.c
@@ -782,10 +782,17 @@  void do_coredump(const kernel_siginfo_t
 		 * filesystem.
 		 */
 		mnt_userns = file_mnt_user_ns(cprm.file);
-		if (!uid_eq(i_uid_into_mnt(mnt_userns, inode), current_fsuid()))
+		if (!uid_eq(i_uid_into_mnt(mnt_userns, inode),
+			    current_fsuid())) {
+			pr_info_ratelimited("Core dump to %s aborted: cannot preserve file owner\n",
+					    cn.corename);
 			goto close_fail;
-		if ((inode->i_mode & 0677) != 0600)
+		}
+		if ((inode->i_mode & 0677) != 0600) {
+			pr_info_ratelimited("Core dump to %s aborted: cannot preserve file permissions\n",
+					    cn.corename);
 			goto close_fail;
+		}
 		if (!(cprm.file->f_mode & FMODE_CAN_WRITE))
 			goto close_fail;
 		if (do_truncate(mnt_userns, cprm.file->f_path.dentry,