From bcf85fcedfdd17911982a3e3564fcfec7b01eebd Mon Sep 17 00:00:00 2001
From: Jann Horn <jannh@google.com>
Date: Thu, 20 Aug 2020 17:42:11 -0700
Subject: [PATCH] romfs: fix uninitialized memory leak in romfs_dev_read()
Git-commit: bcf85fcedfdd17911982a3e3564fcfec7b01eebd
Patch-mainline: v5.9-rc2
References: CVE-2020-29371 bsc#1179429
romfs has a superblock field that limits the size of the filesystem; data
beyond that limit is never accessed.
romfs_dev_read() fetches a caller-supplied number of bytes from the
backing device. It returns 0 on success or an error code on failure;
therefore, its API can't represent short reads, it's all-or-nothing.
However, when romfs_dev_read() detects that the requested operation would
cross the filesystem size limit, it currently silently truncates the
requested number of bytes. This e.g. means that when the content of a
file with size 0x1000 starts one byte before the filesystem size limit,
->readpage() will only fill a single byte of the supplied page while
leaving the rest uninitialized, leaking that uninitialized memory to
userspace.
Fix it by returning an error code instead of truncating the read when the
requested read operation would go beyond the end of the filesystem.
Fixes: da4458bda237 ("NOMMU: Make it possible for RomFS to use MTD devices directly")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: David Howells <dhowells@redhat.com>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200818013202.2246365-1-jannh@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
fs/romfs/storage.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/fs/romfs/storage.c b/fs/romfs/storage.c
index 6b2b4362089e..b57b3ffcbc32 100644
--- a/fs/romfs/storage.c
+++ b/fs/romfs/storage.c
@@ -217,10 +217,8 @@ int romfs_dev_read(struct super_block *sb, unsigned long pos,
size_t limit;
limit = romfs_maxsize(sb);
- if (pos >= limit)
+ if (pos >= limit || buflen > limit - pos)
return -EIO;
- if (buflen > limit - pos)
- buflen = limit - pos;
#ifdef CONFIG_ROMFS_ON_MTD
if (sb->s_mtd)
--
2.26.2