libext2fs: retry reading superblock on open when checksum is bad

When opening a file system which is mounted, it's possible that when
ext2fs_open2() is racing with the kernel modifying the orphaned inode
list, the superblock's checksum could be incorrect.  So retry reading
the superblock in the hopes that the problem will self-correct.

Google-Bug-Id: 151453112
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/lib/ext2fs/openfs.c b/lib/ext2fs/openfs.c
index 51b54a4492eaf67c2d82613ce46fcb7d1b0c0901..ae54870e510296a9bb0c7518ebc48323d0ff193c 100644 (file)
--- a/lib/ext2fs/openfs.c
+++ b/lib/ext2fs/openfs.c
@@ -134,6 +134,7 @@ errcode_t ext2fs_open2(const char *name, const char *io_options,
        int             j;
 #endif
        char            *time_env;
+       int             csum_retries = 0;
 
        EXT2_CHECK_MAGIC(manager, EXT2_ET_MAGIC_IO_MANAGER);
 
@@ -221,6 +222,7 @@ errcode_t ext2fs_open2(const char *name, const char *io_options,
                if (retval)
                        goto cleanup;
        }
+retry:
        retval = io_channel_read_blk(fs->io, superblock, -SUPERBLOCK_SIZE,
                                     fs->super);
        if (retval)
@@ -232,8 +234,11 @@ errcode_t ext2fs_open2(const char *name, const char *io_options,
                retval = 0;
                if (!ext2fs_verify_csum_type(fs, fs->super))
                        retval = EXT2_ET_UNKNOWN_CSUM;
-               if (!ext2fs_superblock_csum_verify(fs, fs->super))
+               if (!ext2fs_superblock_csum_verify(fs, fs->super)) {
+                       if (csum_retries++ < 3)
+                               goto retry;
                        retval = EXT2_ET_SB_CSUM_INVALID;
+               }
        }
 
 #ifdef WORDS_BIGENDIAN