lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Date:   Sun, 30 Aug 2020 21:45:11 -0400
From:   Qian Cai <cai@....pw>
To:     darrick.wong@...cle.com
Cc:     hch@...radead.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Qian Cai <cai@....pw>
Subject: [PATCH v2] iomap: Fix WARN_ON_ONCE() from unprivileged users

It is trivial to trigger a WARN_ON_ONCE(1) in iomap_dio_actor() by
unprivileged users which would taint the kernel, or worse - panic if
panic_on_warn or panic_on_taint is set. Hence, just convert it to
pr_warn_ratelimited() to let users know their workloads are racing.
Thanks Dave Chinner for the initial analysis of the racing reproducers.

Signed-off-by: Qian Cai <cai@....pw>
---

v2: Record the path, pid and command as well.

 fs/iomap/direct-io.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index c1aafb2ab990..66a4502ef675 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -374,6 +374,7 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
 		void *data, struct iomap *iomap, struct iomap *srcmap)
 {
 	struct iomap_dio *dio = data;
+	char pathname[128], *path;
 
 	switch (iomap->type) {
 	case IOMAP_HOLE:
@@ -389,7 +390,21 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length,
 	case IOMAP_INLINE:
 		return iomap_dio_inline_actor(inode, pos, length, dio, iomap);
 	default:
-		WARN_ON_ONCE(1);
+		/*
+		 * DIO is not serialised against mmap() access at all, and so
+		 * if the page_mkwrite occurs between the writeback and the
+		 * iomap_apply() call in the DIO path, then it will see the
+		 * DELALLOC block that the page-mkwrite allocated.
+		 */
+		path = file_path(dio->iocb->ki_filp, pathname,
+				 sizeof(pathname));
+		if (IS_ERR(path))
+			path = "(unknown)";
+
+		pr_warn_ratelimited("page_mkwrite() is racing with DIO read (iomap->type = %u).\n"
+				    "File: %s PID: %d Comm: %.20s\n",
+				    iomap->type, path, current->pid,
+				    current->comm);
 		return -EIO;
 	}
 }
-- 
2.18.4

Powered by blists - more mailing lists