From 0ae0e93624a933a1c6ea4e4680ff5d609f267a43 Mon Sep 17 00:00:00 2001 From: Gabriel Krisman Bertazi Date: Mon, 25 Apr 2022 18:01:00 -0400 Subject: [PATCH] e2fsck: always probe filesystem blocksize with simple io_manager Combining superblock (-b) with undo file (-z) fails iff the block size is not specified (-B) and is different from the first blocksize probed in try_open_fs (1k). The reason is as follows: try_open_fs() will probe different blocksizes if none is provided on the command line. It is done by opening and closing the filesystem until it finds a blocksize that makes sense. This is fine for all io_managers, but undo_io creates the undo file with that blocksize during ext2fs_open. Once try_open_fs realizes it had the wrong blocksize and retries with a different blocksize, undo_io will read the previously created file and think it's corrupt for this filesystem. Ideally, undo_io would know this is a probe and would fix the undo file. It is not simple, though, because it would require undo_io to know the file was just created by the probe code, since an undo file survives through different fsck sessions. We'd have to pass this information around somehow. This seems like a complex change to solve a corner case. Instead, this patch changes the blocksize probe to always use the unix_io_manager. This way, we safely probe for the blocksize without side effects. Once the blocksize is known, we can safely reopen the filesystem under the proper io_manager. An easily reproducer for this issue (from Ted, adapted by me) is: mke2fs -b 4k -q -t ext4 /tmp/foo.img 2G e2fsck -b 32768 -z /tmp/undo /tmp/foo.img Reported-by: Peter Urbanec Signed-off-by: Gabriel Krisman Bertazi Signed-off-by: Theodore Ts'o --- e2fsck/unix.c | 41 ++++++++++++++++++++++++----------------- 1 file changed, 24 insertions(+), 17 deletions(-) diff --git a/e2fsck/unix.c b/e2fsck/unix.c index af57e6a..3708a4d 100644 --- a/e2fsck/unix.c +++ b/e2fsck/unix.c @@ -1171,25 +1171,32 @@ static errcode_t try_open_fs(e2fsck_t ctx, int flags, io_manager io_ptr, errcode_t retval; *ret_fs = NULL; - if (ctx->superblock && ctx->blocksize) { - retval = ext2fs_open2(ctx->filesystem_name, ctx->io_options, - flags, ctx->superblock, ctx->blocksize, - io_ptr, ret_fs); - } else if (ctx->superblock) { - int blocksize; - for (blocksize = EXT2_MIN_BLOCK_SIZE; - blocksize <= EXT2_MAX_BLOCK_SIZE; blocksize *= 2) { - if (*ret_fs) { - ext2fs_free(*ret_fs); - *ret_fs = NULL; + + if (ctx->superblock) { + unsigned long blocksize = ctx->blocksize; + + if (!blocksize) { + for (blocksize = EXT2_MIN_BLOCK_SIZE; + blocksize <= EXT2_MAX_BLOCK_SIZE; blocksize *= 2) { + + retval = ext2fs_open2(ctx->filesystem_name, + ctx->io_options, flags, + ctx->superblock, blocksize, + unix_io_manager, ret_fs); + if (*ret_fs) { + ext2fs_free(*ret_fs); + *ret_fs = NULL; + } + if (!retval) + break; } - retval = ext2fs_open2(ctx->filesystem_name, - ctx->io_options, flags, - ctx->superblock, blocksize, - io_ptr, ret_fs); - if (!retval) - break; + if (retval) + return retval; } + + retval = ext2fs_open2(ctx->filesystem_name, ctx->io_options, + flags, ctx->superblock, blocksize, + io_ptr, ret_fs); } else retval = ext2fs_open2(ctx->filesystem_name, ctx->io_options, flags, 0, 0, io_ptr, ret_fs); -- 1.8.3.1