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-rw-r--r--fs/overlayfs/params.c389
1 files changed, 389 insertions, 0 deletions
diff --git a/fs/overlayfs/params.c b/fs/overlayfs/params.c
new file mode 100644
index 000000000000..d17d6b483dd0
--- /dev/null
+++ b/fs/overlayfs/params.c
@@ -0,0 +1,389 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/fs.h>
+#include <linux/namei.h>
+#include <linux/fs_context.h>
+#include <linux/fs_parser.h>
+#include <linux/posix_acl_xattr.h>
+#include <linux/xattr.h>
+#include "overlayfs.h"
+
+static ssize_t ovl_parse_param_split_lowerdirs(char *str)
+{
+ ssize_t nr_layers = 1, nr_colons = 0;
+ char *s, *d;
+
+ for (s = d = str;; s++, d++) {
+ if (*s == '\\') {
+ s++;
+ } else if (*s == ':') {
+ bool next_colon = (*(s + 1) == ':');
+
+ nr_colons++;
+ if (nr_colons == 2 && next_colon) {
+ pr_err("only single ':' or double '::' sequences of unescaped colons in lowerdir mount option allowed.\n");
+ return -EINVAL;
+ }
+ /* count layers, not colons */
+ if (!next_colon)
+ nr_layers++;
+
+ *d = '\0';
+ continue;
+ }
+
+ *d = *s;
+ if (!*s) {
+ /* trailing colons */
+ if (nr_colons) {
+ pr_err("unescaped trailing colons in lowerdir mount option.\n");
+ return -EINVAL;
+ }
+ break;
+ }
+ nr_colons = 0;
+ }
+
+ return nr_layers;
+}
+
+static int ovl_mount_dir_noesc(const char *name, struct path *path)
+{
+ int err = -EINVAL;
+
+ if (!*name) {
+ pr_err("empty lowerdir\n");
+ goto out;
+ }
+ err = kern_path(name, LOOKUP_FOLLOW, path);
+ if (err) {
+ pr_err("failed to resolve '%s': %i\n", name, err);
+ goto out;
+ }
+ err = -EINVAL;
+ if (ovl_dentry_weird(path->dentry)) {
+ pr_err("filesystem on '%s' not supported\n", name);
+ goto out_put;
+ }
+ if (!d_is_dir(path->dentry)) {
+ pr_err("'%s' not a directory\n", name);
+ goto out_put;
+ }
+ return 0;
+
+out_put:
+ path_put_init(path);
+out:
+ return err;
+}
+
+static void ovl_unescape(char *s)
+{
+ char *d = s;
+
+ for (;; s++, d++) {
+ if (*s == '\\')
+ s++;
+ *d = *s;
+ if (!*s)
+ break;
+ }
+}
+
+static int ovl_mount_dir(const char *name, struct path *path)
+{
+ int err = -ENOMEM;
+ char *tmp = kstrdup(name, GFP_KERNEL);
+
+ if (tmp) {
+ ovl_unescape(tmp);
+ err = ovl_mount_dir_noesc(tmp, path);
+
+ if (!err && path->dentry->d_flags & DCACHE_OP_REAL) {
+ pr_err("filesystem on '%s' not supported as upperdir\n",
+ tmp);
+ path_put_init(path);
+ err = -EINVAL;
+ }
+ kfree(tmp);
+ }
+ return err;
+}
+
+int ovl_parse_param_upperdir(const char *name, struct fs_context *fc,
+ bool workdir)
+{
+ int err;
+ struct ovl_fs *ofs = fc->s_fs_info;
+ struct ovl_config *config = &ofs->config;
+ struct ovl_fs_context *ctx = fc->fs_private;
+ struct path path;
+ char *dup;
+
+ err = ovl_mount_dir(name, &path);
+ if (err)
+ return err;
+
+ /*
+ * Check whether upper path is read-only here to report failures
+ * early. Don't forget to recheck when the superblock is created
+ * as the mount attributes could change.
+ */
+ if (__mnt_is_readonly(path.mnt)) {
+ path_put(&path);
+ return -EINVAL;
+ }
+
+ dup = kstrdup(name, GFP_KERNEL);
+ if (!dup) {
+ path_put(&path);
+ return -ENOMEM;
+ }
+
+ if (workdir) {
+ kfree(config->workdir);
+ config->workdir = dup;
+ path_put(&ctx->work);
+ ctx->work = path;
+ } else {
+ kfree(config->upperdir);
+ config->upperdir = dup;
+ path_put(&ctx->upper);
+ ctx->upper = path;
+ }
+ return 0;
+}
+
+void ovl_parse_param_drop_lowerdir(struct ovl_fs_context *ctx)
+{
+ for (size_t nr = 0; nr < ctx->nr; nr++) {
+ path_put(&ctx->lower[nr].path);
+ kfree(ctx->lower[nr].name);
+ ctx->lower[nr].name = NULL;
+ }
+ ctx->nr = 0;
+ ctx->nr_data = 0;
+}
+
+/*
+ * Parse lowerdir= mount option:
+ *
+ * (1) lowerdir=/lower1:/lower2:/lower3::/data1::/data2
+ * Set "/lower1", "/lower2", and "/lower3" as lower layers and
+ * "/data1" and "/data2" as data lower layers. Any existing lower
+ * layers are replaced.
+ * (2) lowerdir=:/lower4
+ * Append "/lower4" to current stack of lower layers. This requires
+ * that there already is at least one lower layer configured.
+ * (3) lowerdir=::/lower5
+ * Append data "/lower5" as data lower layer. This requires that
+ * there's at least one regular lower layer present.
+ */
+int ovl_parse_param_lowerdir(const char *name, struct fs_context *fc)
+{
+ int err;
+ struct ovl_fs_context *ctx = fc->fs_private;
+ struct ovl_fs_context_layer *l;
+ char *dup = NULL, *dup_iter;
+ ssize_t nr_lower = 0, nr = 0, nr_data = 0;
+ bool append = false, data_layer = false;
+
+ /*
+ * Ensure we're backwards compatible with mount(2)
+ * by allowing relative paths.
+ */
+
+ /* drop all existing lower layers */
+ if (!*name) {
+ ovl_parse_param_drop_lowerdir(ctx);
+ return 0;
+ }
+
+ if (strncmp(name, "::", 2) == 0) {
+ /*
+ * This is a data layer.
+ * There must be at least one regular lower layer
+ * specified.
+ */
+ if (ctx->nr == 0) {
+ pr_err("data lower layers without regular lower layers not allowed");
+ return -EINVAL;
+ }
+
+ /* Skip the leading "::". */
+ name += 2;
+ data_layer = true;
+ /*
+ * A data layer is automatically an append as there
+ * must've been at least one regular lower layer.
+ */
+ append = true;
+ } else if (*name == ':') {
+ /*
+ * This is a regular lower layer.
+ * If users want to append a layer enforce that they
+ * have already specified a first layer before. It's
+ * better to be strict.
+ */
+ if (ctx->nr == 0) {
+ pr_err("cannot append layer if no previous layer has been specified");
+ return -EINVAL;
+ }
+
+ /*
+ * Once a sequence of data layers has started regular
+ * lower layers are forbidden.
+ */
+ if (ctx->nr_data > 0) {
+ pr_err("regular lower layers cannot follow data lower layers");
+ return -EINVAL;
+ }
+
+ /* Skip the leading ":". */
+ name++;
+ append = true;
+ }
+
+ dup = kstrdup(name, GFP_KERNEL);
+ if (!dup)
+ return -ENOMEM;
+
+ err = -EINVAL;
+ nr_lower = ovl_parse_param_split_lowerdirs(dup);
+ if (nr_lower < 0)
+ goto out_err;
+
+ if ((nr_lower > OVL_MAX_STACK) ||
+ (append && (size_add(ctx->nr, nr_lower) > OVL_MAX_STACK))) {
+ pr_err("too many lower directories, limit is %d\n", OVL_MAX_STACK);
+ goto out_err;
+ }
+
+ if (!append)
+ ovl_parse_param_drop_lowerdir(ctx);
+
+ /*
+ * (1) append
+ *
+ * We want nr <= nr_lower <= capacity We know nr > 0 and nr <=
+ * capacity. If nr == 0 this wouldn't be append. If nr +
+ * nr_lower is <= capacity then nr <= nr_lower <= capacity
+ * already holds. If nr + nr_lower exceeds capacity, we realloc.
+ *
+ * (2) replace
+ *
+ * Ensure we're backwards compatible with mount(2) which allows
+ * "lowerdir=/a:/b:/c,lowerdir=/d:/e:/f" causing the last
+ * specified lowerdir mount option to win.
+ *
+ * We want nr <= nr_lower <= capacity We know either (i) nr == 0
+ * or (ii) nr > 0. We also know nr_lower > 0. The capacity
+ * could've been changed multiple times already so we only know
+ * nr <= capacity. If nr + nr_lower > capacity we realloc,
+ * otherwise nr <= nr_lower <= capacity holds already.
+ */
+ nr_lower += ctx->nr;
+ if (nr_lower > ctx->capacity) {
+ err = -ENOMEM;
+ l = krealloc_array(ctx->lower, nr_lower, sizeof(*ctx->lower),
+ GFP_KERNEL_ACCOUNT);
+ if (!l)
+ goto out_err;
+
+ ctx->lower = l;
+ ctx->capacity = nr_lower;
+ }
+
+ /*
+ * (3) By (1) and (2) we know nr <= nr_lower <= capacity.
+ * (4) If ctx->nr == 0 => replace
+ * We have verified above that the lowerdir mount option
+ * isn't an append, i.e., the lowerdir mount option
+ * doesn't start with ":" or "::".
+ * (4.1) The lowerdir mount options only contains regular lower
+ * layers ":".
+ * => Nothing to verify.
+ * (4.2) The lowerdir mount options contains regular ":" and
+ * data "::" layers.
+ * => We need to verify that data lower layers "::" aren't
+ * followed by regular ":" lower layers
+ * (5) If ctx->nr > 0 => append
+ * We know that there's at least one regular layer
+ * otherwise we would've failed when parsing the previous
+ * lowerdir mount option.
+ * (5.1) The lowerdir mount option is a regular layer ":" append
+ * => We need to verify that no data layers have been
+ * specified before.
+ * (5.2) The lowerdir mount option is a data layer "::" append
+ * We know that there's at least one regular layer or
+ * other data layers. => There's nothing to verify.
+ */
+ dup_iter = dup;
+ for (nr = ctx->nr; nr < nr_lower; nr++) {
+ l = &ctx->lower[nr];
+ memset(l, 0, sizeof(*l));
+
+ err = ovl_mount_dir_noesc(dup_iter, &l->path);
+ if (err)
+ goto out_put;
+
+ err = -ENOMEM;
+ l->name = kstrdup(dup_iter, GFP_KERNEL_ACCOUNT);
+ if (!l->name)
+ goto out_put;
+
+ if (data_layer)
+ nr_data++;
+
+ /* Calling strchr() again would overrun. */
+ if ((nr + 1) == nr_lower)
+ break;
+
+ err = -EINVAL;
+ dup_iter = strchr(dup_iter, '\0') + 1;
+ if (*dup_iter) {
+ /*
+ * This is a regular layer so we require that
+ * there are no data layers.
+ */
+ if ((ctx->nr_data + nr_data) > 0) {
+ pr_err("regular lower layers cannot follow data lower layers");
+ goto out_put;
+ }
+
+ data_layer = false;
+ continue;
+ }
+
+ /* This is a data lower layer. */
+ data_layer = true;
+ dup_iter++;
+ }
+ ctx->nr = nr_lower;
+ ctx->nr_data += nr_data;
+ kfree(dup);
+ return 0;
+
+out_put:
+ /*
+ * We know nr >= ctx->nr < nr_lower. If we failed somewhere
+ * we want to undo until nr == ctx->nr. This is correct for
+ * both ctx->nr == 0 and ctx->nr > 0.
+ */
+ for (; nr >= ctx->nr; nr--) {
+ l = &ctx->lower[nr];
+ kfree(l->name);
+ l->name = NULL;
+ path_put(&l->path);
+
+ /* don't overflow */
+ if (nr == 0)
+ break;
+ }
+
+out_err:
+ kfree(dup);
+
+ /* Intentionally don't realloc to a smaller size. */
+ return err;
+}
generated by cgit (git 2.34.1) at 2024-06-21 16:00:09 +0000