ovl: fix memory leak in ovl_parse_param()

On failure to parse parameters in ovl_parse_param_lowerdir(), it is
necessary to update ctx->nr with the correct nr before using
ovl_reset_lowerdirs() to release l->name.

Reported-and-tested-by: syzbot+26eedf3631650972f17c@syzkaller.appspotmail.com
Fixes: c835110b588a ("ovl: remove unused code in lowerdir param parsing")
Co-authored-by: Edward Adam Davis <eadavis@qq.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

diff --git a/fs/overlayfs/params.c b/fs/overlayfs/params.c
index ddab9ea267d1283b73f8245aa1adb81232f2a202..3fe2dde1598f9ead48dbbaafcd2c9660fd358f00 100644 (file)
--- a/fs/overlayfs/params.c
+++ b/fs/overlayfs/params.c
@@ -430,7 +430,7 @@ static int ovl_parse_param_lowerdir(const char *name, struct fs_context *fc)
        struct ovl_fs_context *ctx = fc->fs_private;
        struct ovl_fs_context_layer *l;
        char *dup = NULL, *iter;
-       ssize_t nr_lower = 0, nr = 0, nr_data = 0;
+       ssize_t nr_lower, nr;
        bool data_layer = false;
 
        /*
@@ -482,6 +482,7 @@ static int ovl_parse_param_lowerdir(const char *name, struct fs_context *fc)
        iter = dup;
        l = ctx->lower;
        for (nr = 0; nr < nr_lower; nr++, l++) {
+               ctx->nr++;
                memset(l, 0, sizeof(*l));
 
                err = ovl_mount_dir(iter, &l->path);
@@ -498,10 +499,10 @@ static int ovl_parse_param_lowerdir(const char *name, struct fs_context *fc)
                        goto out_put;
 
                if (data_layer)
-                       nr_data++;
+                       ctx->nr_data++;
 
                /* Calling strchr() again would overrun. */
-               if ((nr + 1) == nr_lower)
+               if (ctx->nr == nr_lower)
                        break;
 
                err = -EINVAL;
@@ -511,7 +512,7 @@ static int ovl_parse_param_lowerdir(const char *name, struct fs_context *fc)
                         * This is a regular layer so we require that
                         * there are no data layers.
                         */
-                       if ((ctx->nr_data + nr_data) > 0) {
+                       if (ctx->nr_data > 0) {
                                pr_err("regular lower layers cannot follow data lower layers");
                                goto out_put;
                        }
@@ -524,8 +525,6 @@ static int ovl_parse_param_lowerdir(const char *name, struct fs_context *fc)
                data_layer = true;
                iter++;
        }
-       ctx->nr = nr_lower;
-       ctx->nr_data += nr_data;
        kfree(dup);
        return 0;