Messages in this thread Patch in this message | | | Date | Tue, 20 Nov 2012 12:42:38 -0800 | From | Kees Cook <> | Subject | [PATCH v2] devtmpfs: mount with noexec and nosuid |
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Since devtmpfs is writable, make the default noexec,nosuid as well. This protects from the case of a privileged process having an arbitrary file write flaw and an argumentless arbitrary execution (i.e. it would lack the ability to run "mount -o remount,exec,suid /dev").
Cc: ellyjones@chromium.org Cc: Kay Sievers <kay@vrfy.org> Cc: Roland Eggner <edvx1@systemanalysen.net> Signed-off-by: Kees Cook <keescook@chromium.org>
--- v2: - use CONFIG_DEVTMPFS_SAFE to wrap the logic. --- drivers/base/Kconfig | 12 ++++++++++++ drivers/base/devtmpfs.c | 12 ++++++++++-- 2 files changed, 22 insertions(+), 2 deletions(-)
diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig index b34b5cd..a37fcf2 100644 --- a/drivers/base/Kconfig +++ b/drivers/base/Kconfig @@ -56,6 +56,18 @@ config DEVTMPFS_MOUNT rescue mode with init=/bin/sh, even when the /dev directory on the rootfs is completely empty. +config DEVTMPFS_SAFE + bool "Use nosuid,noexec mount options on devtmpfs" + depends on DEVTMPFS + help + This instructs the kernel to include the MS_NOEXEC and + MS_NOSUID mount flags when mounting devtmpfs. This prevents + certain kinds of code-execution attacks on embedded platforms. + + Notice: If enabled, things like /dev/mem cannot be mmapped + with the PROT_EXEC flag. This can break, for example, non-KMS + video drivers. + config STANDALONE bool "Select only drivers that don't need compile-time external firmware" if EXPERIMENTAL default y diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c index 147d1a4..bf85fbf 100644 --- a/drivers/base/devtmpfs.c +++ b/drivers/base/devtmpfs.c @@ -340,6 +340,10 @@ static int handle_remove(const char *nodename, struct device *dev) int devtmpfs_mount(const char *mntdir) { int err; + int mflags = MS_SILENT; +#ifdef CONFIG_DEVTMPFS_SAFE + mflags |= MS_NOEXEC | MS_NOSUID; +#endif if (!mount_dev) return 0; @@ -347,7 +351,7 @@ int devtmpfs_mount(const char *mntdir) if (!thread) return 0; - err = sys_mount("devtmpfs", (char *)mntdir, "devtmpfs", MS_SILENT, NULL); + err = sys_mount("devtmpfs", (char *)mntdir, "devtmpfs", mflags, NULL); if (err) printk(KERN_INFO "devtmpfs: error mounting %i\n", err); else @@ -369,10 +373,14 @@ static int devtmpfsd(void *p) { char options[] = "mode=0755"; int *err = p; + int mflags = MS_SILENT; +#ifdef CONFIG_DEVTMPFS_SAFE + mflags |= MS_NOEXEC | MS_NOSUID; +#endif *err = sys_unshare(CLONE_NEWNS); if (*err) goto out; - *err = sys_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, options); + *err = sys_mount("devtmpfs", "/", "devtmpfs", mflags, options); if (*err) goto out; sys_chdir("/.."); /* will traverse into overmounted root */ -- 1.7.9.5
-- Kees Cook Chrome OS Security
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