Fix CVE-2015-8785: fuse infinite loop

diff --git a/CVE-2015-8785-fuse-break-infinite-loop-in-fuse_fill_write_pages.patch b/CVE-2015-8785-fuse-break-infinite-loop-in-fuse_fill_write_pages.patch
new file mode 100644 (file)
index 0000000..f96b96f
--- /dev/null
+++ b/CVE-2015-8785-fuse-break-infinite-loop-in-fuse_fill_write_pages.patch
@@ -0,0 +1,61 @@
+From 3ca8138f014a913f98e6ef40e939868e1e9ea876 Mon Sep 17 00:00:00 2001
+From: Roman Gushchin <klamm@yandex-team.ru>
+Date: Mon, 12 Oct 2015 16:33:44 +0300
+Subject: [PATCH] fuse: break infinite loop in fuse_fill_write_pages()
+
+I got a report about unkillable task eating CPU. Further
+investigation shows, that the problem is in the fuse_fill_write_pages()
+function. If iov's first segment has zero length, we get an infinite
+loop, because we never reach iov_iter_advance() call.
+
+Fix this by calling iov_iter_advance() before repeating an attempt to
+copy data from userspace.
+
+A similar problem is described in 124d3b7041f ("fix writev regression:
+pan hanging unkillable and un-straceable"). If zero-length segmend
+is followed by segment with invalid address,
+iov_iter_fault_in_readable() checks only first segment (zero-length),
+iov_iter_copy_from_user_atomic() skips it, fails at second and
+returns zero -> goto again without skipping zero-length segment.
+
+Patch calls iov_iter_advance() before goto again: we'll skip zero-length
+segment at second iteraction and iov_iter_fault_in_readable() will detect
+invalid address.
+
+Special thanks to Konstantin Khlebnikov, who helped a lot with the commit
+description.
+
+Cc: Andrew Morton <akpm@linux-foundation.org>
+Cc: Maxim Patlasov <mpatlasov@parallels.com>
+Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
+Signed-off-by: Roman Gushchin <klamm@yandex-team.ru>
+Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
+Fixes: ea9b9907b82a ("fuse: implement perform_write")
+Cc: <stable@vger.kernel.org>
+---
+ fs/fuse/file.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/fs/fuse/file.c b/fs/fuse/file.c
+index f523f2f..195476a 100644
+--- a/fs/fuse/file.c
++++ b/fs/fuse/file.c
+@@ -1049,6 +1049,7 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req,
+               tmp = iov_iter_copy_from_user_atomic(page, ii, offset, bytes);
+               flush_dcache_page(page);
+ 
++              iov_iter_advance(ii, tmp);
+               if (!tmp) {
+                       unlock_page(page);
+                       page_cache_release(page);
+@@ -1061,7 +1062,6 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req,
+               req->page_descs[req->num_pages].length = tmp;
+               req->num_pages++;
+ 
+-              iov_iter_advance(ii, tmp);
+               count += tmp;
+               pos += tmp;
+               offset += tmp;
+-- 
+2.1.4
+

diff --git a/Makefile b/Makefile
index bd9e0ff08dc678ec7b5f9b196cce89ecba13a1ec..2866654088450d14f23c96b4e70f9e47fb179d46 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -241,6 +241,7 @@ ${KERNEL_SRC}/README ${KERNEL_CFG_ORG}: ${KERNELSRCTAR}
        cd ${KERNEL_SRC}; patch -p1 <../kvm-x86-obey-KVM_X86_QUIRK_CD_NW_CLEARED-in-kvm_set_cr0.patch
        cd ${KERNEL_SRC}; patch -p1 <../apparmor-socket-mediation.patch
        cd ${KERNEL_SRC}; patch -p1 <../CVE-2015-7513-KVM-x86-Reload-pit-counters-for-all-channels.patch
+       cd ${KERNEL_SRC}; patch -p1 <../CVE-2015-8785-fuse-break-infinite-loop-in-fuse_fill_write_pages.patch
        # backport iSCSI fix from 4.4rc5
        cd ${KERNEL_SRC}; patch -p1 <../iSCSI-block-sd-Fix-device-imposed-transfer-length-limits.patch
        # backport aacraid update from kernel 4.4rc5