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authorLinus Torvalds <torvalds@linux-foundation.org>2017-12-15 12:46:48 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2017-12-15 12:46:48 -0800
commit227701e0e7078065f24f5a6ca220218fd80023a5 (patch)
tree6cf2337d3a9a57f81c7e96278fceb505256327b8
parent06f976ecc7afbf2e68c44ec9e591af4ceca04ca6 (diff)
parentda2e6b7eeda8919f677c790ef51161dd02e513a6 (diff)
downloadlinux-sh-227701e0e7078065f24f5a6ca220218fd80023a5.tar.gz
Merge branch 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs
Pull overlayfs fixes from Miklos Szeredi: - fix incomplete syncing of filesystem - fix regression in readdir on ovl over 9p - only follow redirects when needed - misc fixes and cleanups * 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs: ovl: fix overlay: warning prefix ovl: Use PTR_ERR_OR_ZERO() ovl: Sync upper dirty data when syncing overlayfs ovl: update ctx->pos on impure dir iteration ovl: Pass ovl_get_nlink() parameters in right order ovl: don't follow redirects if redirect_dir=off
-rw-r--r--Documentation/filesystems/overlayfs.txt34
-rw-r--r--fs/overlayfs/Kconfig10
-rw-r--r--fs/overlayfs/dir.c3
-rw-r--r--fs/overlayfs/namei.c18
-rw-r--r--fs/overlayfs/overlayfs.h2
-rw-r--r--fs/overlayfs/ovl_entry.h2
-rw-r--r--fs/overlayfs/readdir.c7
-rw-r--r--fs/overlayfs/super.c87
8 files changed, 137 insertions, 26 deletions
diff --git a/Documentation/filesystems/overlayfs.txt b/Documentation/filesystems/overlayfs.txt
index 8caa60734647..e6a5f4912b6d 100644
--- a/Documentation/filesystems/overlayfs.txt
+++ b/Documentation/filesystems/overlayfs.txt
@@ -156,6 +156,40 @@ handle it in two different ways:
root of the overlay. Finally the directory is moved to the new
location.
+There are several ways to tune the "redirect_dir" feature.
+
+Kernel config options:
+
+- OVERLAY_FS_REDIRECT_DIR:
+ If this is enabled, then redirect_dir is turned on by default.
+- OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW:
+ If this is enabled, then redirects are always followed by default. Enabling
+ this results in a less secure configuration. Enable this option only when
+ worried about backward compatibility with kernels that have the redirect_dir
+ feature and follow redirects even if turned off.
+
+Module options (can also be changed through /sys/module/overlay/parameters/*):
+
+- "redirect_dir=BOOL":
+ See OVERLAY_FS_REDIRECT_DIR kernel config option above.
+- "redirect_always_follow=BOOL":
+ See OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW kernel config option above.
+- "redirect_max=NUM":
+ The maximum number of bytes in an absolute redirect (default is 256).
+
+Mount options:
+
+- "redirect_dir=on":
+ Redirects are enabled.
+- "redirect_dir=follow":
+ Redirects are not created, but followed.
+- "redirect_dir=off":
+ Redirects are not created and only followed if "redirect_always_follow"
+ feature is enabled in the kernel/module config.
+- "redirect_dir=nofollow":
+ Redirects are not created and not followed (equivalent to "redirect_dir=off"
+ if "redirect_always_follow" feature is not enabled).
+
Non-directories
---------------
diff --git a/fs/overlayfs/Kconfig b/fs/overlayfs/Kconfig
index cbfc196e5dc5..5ac415466861 100644
--- a/fs/overlayfs/Kconfig
+++ b/fs/overlayfs/Kconfig
@@ -24,6 +24,16 @@ config OVERLAY_FS_REDIRECT_DIR
an overlay which has redirects on a kernel that doesn't support this
feature will have unexpected results.
+config OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW
+ bool "Overlayfs: follow redirects even if redirects are turned off"
+ default y
+ depends on OVERLAY_FS
+ help
+ Disable this to get a possibly more secure configuration, but that
+ might not be backward compatible with previous kernels.
+
+ For more information, see Documentation/filesystems/overlayfs.txt
+
config OVERLAY_FS_INDEX
bool "Overlayfs: turn on inodes index feature by default"
depends on OVERLAY_FS
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index e13921824c70..f9788bc116a8 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -887,7 +887,8 @@ static int ovl_set_redirect(struct dentry *dentry, bool samedir)
spin_unlock(&dentry->d_lock);
} else {
kfree(redirect);
- pr_warn_ratelimited("overlay: failed to set redirect (%i)\n", err);
+ pr_warn_ratelimited("overlayfs: failed to set redirect (%i)\n",
+ err);
/* Fall back to userspace copy-up */
err = -EXDEV;
}
diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index 625ed8066570..beb945e1963c 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -435,7 +435,7 @@ int ovl_verify_index(struct dentry *index, struct ovl_path *lower,
/* Check if index is orphan and don't warn before cleaning it */
if (d_inode(index)->i_nlink == 1 &&
- ovl_get_nlink(index, origin.dentry, 0) == 0)
+ ovl_get_nlink(origin.dentry, index, 0) == 0)
err = -ENOENT;
dput(origin.dentry);
@@ -681,6 +681,22 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
if (d.stop)
break;
+ /*
+ * Following redirects can have security consequences: it's like
+ * a symlink into the lower layer without the permission checks.
+ * This is only a problem if the upper layer is untrusted (e.g
+ * comes from an USB drive). This can allow a non-readable file
+ * or directory to become readable.
+ *
+ * Only following redirects when redirects are enabled disables
+ * this attack vector when not necessary.
+ */
+ err = -EPERM;
+ if (d.redirect && !ofs->config.redirect_follow) {
+ pr_warn_ratelimited("overlay: refusing to follow redirect for (%pd2)\n", dentry);
+ goto out_put;
+ }
+
if (d.redirect && d.redirect[0] == '/' && poe != roe) {
poe = roe;
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 13eab09a6b6f..b489099ccd49 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -180,7 +180,7 @@ static inline int ovl_do_whiteout(struct inode *dir, struct dentry *dentry)
static inline struct dentry *ovl_do_tmpfile(struct dentry *dentry, umode_t mode)
{
struct dentry *ret = vfs_tmpfile(dentry, mode, 0);
- int err = IS_ERR(ret) ? PTR_ERR(ret) : 0;
+ int err = PTR_ERR_OR_ZERO(ret);
pr_debug("tmpfile(%pd2, 0%o) = %i\n", dentry, mode, err);
return ret;
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index 752bab645879..9d0bc03bf6e4 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -14,6 +14,8 @@ struct ovl_config {
char *workdir;
bool default_permissions;
bool redirect_dir;
+ bool redirect_follow;
+ const char *redirect_mode;
bool index;
};
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 0daa4354fec4..8c98578d27a1 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -499,7 +499,7 @@ out:
return err;
fail:
- pr_warn_ratelimited("overlay: failed to look up (%s) for ino (%i)\n",
+ pr_warn_ratelimited("overlayfs: failed to look up (%s) for ino (%i)\n",
p->name, err);
goto out;
}
@@ -663,7 +663,10 @@ static int ovl_iterate_real(struct file *file, struct dir_context *ctx)
return PTR_ERR(rdt.cache);
}
- return iterate_dir(od->realfile, &rdt.ctx);
+ err = iterate_dir(od->realfile, &rdt.ctx);
+ ctx->pos = rdt.ctx.pos;
+
+ return err;
}
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 288d20f9a55a..76440feb79f6 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -33,6 +33,13 @@ module_param_named(redirect_dir, ovl_redirect_dir_def, bool, 0644);
MODULE_PARM_DESC(ovl_redirect_dir_def,
"Default to on or off for the redirect_dir feature");
+static bool ovl_redirect_always_follow =
+ IS_ENABLED(CONFIG_OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW);
+module_param_named(redirect_always_follow, ovl_redirect_always_follow,
+ bool, 0644);
+MODULE_PARM_DESC(ovl_redirect_always_follow,
+ "Follow redirects even if redirect_dir feature is turned off");
+
static bool ovl_index_def = IS_ENABLED(CONFIG_OVERLAY_FS_INDEX);
module_param_named(index, ovl_index_def, bool, 0644);
MODULE_PARM_DESC(ovl_index_def,
@@ -232,6 +239,7 @@ static void ovl_free_fs(struct ovl_fs *ofs)
kfree(ofs->config.lowerdir);
kfree(ofs->config.upperdir);
kfree(ofs->config.workdir);
+ kfree(ofs->config.redirect_mode);
if (ofs->creator_cred)
put_cred(ofs->creator_cred);
kfree(ofs);
@@ -244,6 +252,7 @@ static void ovl_put_super(struct super_block *sb)
ovl_free_fs(ofs);
}
+/* Sync real dirty inodes in upper filesystem (if it exists) */
static int ovl_sync_fs(struct super_block *sb, int wait)
{
struct ovl_fs *ofs = sb->s_fs_info;
@@ -252,14 +261,24 @@ static int ovl_sync_fs(struct super_block *sb, int wait)
if (!ofs->upper_mnt)
return 0;
- upper_sb = ofs->upper_mnt->mnt_sb;
- if (!upper_sb->s_op->sync_fs)
+
+ /*
+ * If this is a sync(2) call or an emergency sync, all the super blocks
+ * will be iterated, including upper_sb, so no need to do anything.
+ *
+ * If this is a syncfs(2) call, then we do need to call
+ * sync_filesystem() on upper_sb, but enough if we do it when being
+ * called with wait == 1.
+ */
+ if (!wait)
return 0;
- /* real inodes have already been synced by sync_filesystem(ovl_sb) */
+ upper_sb = ofs->upper_mnt->mnt_sb;
+
down_read(&upper_sb->s_umount);
- ret = upper_sb->s_op->sync_fs(upper_sb, wait);
+ ret = sync_filesystem(upper_sb);
up_read(&upper_sb->s_umount);
+
return ret;
}
@@ -295,6 +314,11 @@ static bool ovl_force_readonly(struct ovl_fs *ofs)
return (!ofs->upper_mnt || !ofs->workdir);
}
+static const char *ovl_redirect_mode_def(void)
+{
+ return ovl_redirect_dir_def ? "on" : "off";
+}
+
/**
* ovl_show_options
*
@@ -313,12 +337,10 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
}
if (ofs->config.default_permissions)
seq_puts(m, ",default_permissions");
- if (ofs->config.redirect_dir != ovl_redirect_dir_def)
- seq_printf(m, ",redirect_dir=%s",
- ofs->config.redirect_dir ? "on" : "off");
+ if (strcmp(ofs->config.redirect_mode, ovl_redirect_mode_def()) != 0)
+ seq_printf(m, ",redirect_dir=%s", ofs->config.redirect_mode);
if (ofs->config.index != ovl_index_def)
- seq_printf(m, ",index=%s",
- ofs->config.index ? "on" : "off");
+ seq_printf(m, ",index=%s", ofs->config.index ? "on" : "off");
return 0;
}
@@ -348,8 +370,7 @@ enum {
OPT_UPPERDIR,
OPT_WORKDIR,
OPT_DEFAULT_PERMISSIONS,
- OPT_REDIRECT_DIR_ON,
- OPT_REDIRECT_DIR_OFF,
+ OPT_REDIRECT_DIR,
OPT_INDEX_ON,
OPT_INDEX_OFF,
OPT_ERR,
@@ -360,8 +381,7 @@ static const match_table_t ovl_tokens = {
{OPT_UPPERDIR, "upperdir=%s"},
{OPT_WORKDIR, "workdir=%s"},
{OPT_DEFAULT_PERMISSIONS, "default_permissions"},
- {OPT_REDIRECT_DIR_ON, "redirect_dir=on"},
- {OPT_REDIRECT_DIR_OFF, "redirect_dir=off"},
+ {OPT_REDIRECT_DIR, "redirect_dir=%s"},
{OPT_INDEX_ON, "index=on"},
{OPT_INDEX_OFF, "index=off"},
{OPT_ERR, NULL}
@@ -390,10 +410,37 @@ static char *ovl_next_opt(char **s)
return sbegin;
}
+static int ovl_parse_redirect_mode(struct ovl_config *config, const char *mode)
+{
+ if (strcmp(mode, "on") == 0) {
+ config->redirect_dir = true;
+ /*
+ * Does not make sense to have redirect creation without
+ * redirect following.
+ */
+ config->redirect_follow = true;
+ } else if (strcmp(mode, "follow") == 0) {
+ config->redirect_follow = true;
+ } else if (strcmp(mode, "off") == 0) {
+ if (ovl_redirect_always_follow)
+ config->redirect_follow = true;
+ } else if (strcmp(mode, "nofollow") != 0) {
+ pr_err("overlayfs: bad mount option \"redirect_dir=%s\"\n",
+ mode);
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
static int ovl_parse_opt(char *opt, struct ovl_config *config)
{
char *p;
+ config->redirect_mode = kstrdup(ovl_redirect_mode_def(), GFP_KERNEL);
+ if (!config->redirect_mode)
+ return -ENOMEM;
+
while ((p = ovl_next_opt(&opt)) != NULL) {
int token;
substring_t args[MAX_OPT_ARGS];
@@ -428,12 +475,11 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
config->default_permissions = true;
break;
- case OPT_REDIRECT_DIR_ON:
- config->redirect_dir = true;
- break;
-
- case OPT_REDIRECT_DIR_OFF:
- config->redirect_dir = false;
+ case OPT_REDIRECT_DIR:
+ kfree(config->redirect_mode);
+ config->redirect_mode = match_strdup(&args[0]);
+ if (!config->redirect_mode)
+ return -ENOMEM;
break;
case OPT_INDEX_ON:
@@ -458,7 +504,7 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
config->workdir = NULL;
}
- return 0;
+ return ovl_parse_redirect_mode(config, config->redirect_mode);
}
#define OVL_WORKDIR_NAME "work"
@@ -1160,7 +1206,6 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
if (!cred)
goto out_err;
- ofs->config.redirect_dir = ovl_redirect_dir_def;
ofs->config.index = ovl_index_def;
err = ovl_parse_opt((char *) data, &ofs->config);
if (err)