fs/squashfs: sqfs_read: Prevent arbitrary code execution

Following Jincheng's report, an out-of-band write leading to arbitrary
code execution is possible because on one side the squashfs logic
accepts directory names up to 65535 bytes (u16), while U-Boot fs logic
accepts directory names up to 255 bytes long.

Prevent such an exploit from happening by capping directory name sizes
to 255. Use a define for this purpose so that developers can link the
limitation to its source and eventually kill it some day by dynamically
allocating this array (if ever desired).

Link: https://lore.kernel.org/all/CALO=DHFB+yBoXxVr5KcsK0iFdg+e7ywko4-e+72kjbcS8JBfPw@mail.gmail.com
Reported-by: Jincheng Wang <jc.w4ng@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Tested-by: Jincheng Wang <jc.w4ng@gmail.com>

diff --git a/fs/squashfs/sqfs.c b/fs/squashfs/sqfs.c
index 547d2fd4b3025d251232d27858238bc8fea0a584..b9f05efd9c9c525e1118877e278800c159a14dcd 100644 (file)
--- a/fs/squashfs/sqfs.c
+++ b/fs/squashfs/sqfs.c
@@ -975,6 +975,7 @@ int sqfs_readdir(struct fs_dir_stream *fs_dirs, struct fs_dirent **dentp)
        int i_number, offset = 0, ret;
        struct fs_dirent *dent;
        unsigned char *ipos;
+       u16 name_size;
 
        dirs = (struct squashfs_dir_stream *)fs_dirs;
        if (!dirs->size) {
@@ -1057,9 +1058,10 @@ int sqfs_readdir(struct fs_dir_stream *fs_dirs, struct fs_dirent **dentp)
                return -SQFS_STOP_READDIR;
        }
 
-       /* Set entry name */
-       strncpy(dent->name, dirs->entry->name, dirs->entry->name_size + 1);
-       dent->name[dirs->entry->name_size + 1] = '\0';
+       /* Set entry name (capped at FS_DIRENT_NAME_LEN which is a U-Boot limitation) */
+       name_size = min_t(u16, dirs->entry->name_size + 1, FS_DIRENT_NAME_LEN - 1);
+       strncpy(dent->name, dirs->entry->name, name_size);
+       dent->name[name_size] = '\0';
 
        offset = dirs->entry->name_size + 1 + SQFS_ENTRY_BASE_LENGTH;
        dirs->entry_count--;

diff --git a/include/fs.h b/include/fs.h
index b43f16a692ff013e55c0cc5ca76a903c975302b4..2195dc172ece5871f05369723f390057e179988b 100644 (file)
--- a/include/fs.h
+++ b/include/fs.h
@@ -174,6 +174,8 @@ int fs_write(const char *filename, ulong addr, loff_t offset, loff_t len,
 #define FS_DT_REG  8         /* regular file */
 #define FS_DT_LNK  10        /* symbolic link */
 
+#define FS_DIRENT_NAME_LEN 256
+
 /**
  * struct fs_dirent - directory entry
  *
@@ -194,7 +196,7 @@ struct fs_dirent {
        /** change_time:        time of last modification */
        struct rtc_time change_time;
        /** name:               file name */
-       char name[256];
+       char name[FS_DIRENT_NAME_LEN];
 };
 
 /* Note: fs_dir_stream should be treated as opaque to the user of fs layer */