From 40f705a736eac10e7dca7ab5dd5ed675a6df031d Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Wed, 9 Sep 2015 15:38:30 -0700 Subject: [PATCH] fs: Don't dump core if the corefile would become world-readable. On a filesystem like vfat, all files are created with the same owner and mode independent of who created the file. When a vfat filesystem is mounted with root as owner of all files and read access for everyone, root's processes left world-readable coredumps on it (but other users' processes only left empty corefiles when given write access because of the uid mismatch). Given that the old behavior was inconsistent and insecure, I don't see a problem with changing it. Now, all processes refuse to dump core unless the resulting corefile will only be readable by their owner. Signed-off-by: Jann Horn Acked-by: Kees Cook Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/coredump.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/fs/coredump.c b/fs/coredump.c index b696dc2c220d..a8f75640ac86 100644 --- a/fs/coredump.c +++ b/fs/coredump.c @@ -685,11 +685,15 @@ void do_coredump(const siginfo_t *siginfo) if (!S_ISREG(inode->i_mode)) goto close_fail; /* - * Dont allow local users get cute and trick others to coredump - * into their pre-created files. + * Don't dump core if the filesystem changed owner or mode + * of the file during file creation. This is an issue when + * a process dumps core while its cwd is e.g. on a vfat + * filesystem. */ if (!uid_eq(inode->i_uid, current_fsuid())) goto close_fail; + if ((inode->i_mode & 0677) != 0600) + goto close_fail; if (!(cprm.file->f_mode & FMODE_CAN_WRITE)) goto close_fail; if (do_truncate(cprm.file->f_path.dentry, 0, 0, cprm.file)) -- 2.20.1