e2fsprogs: dblist iteration loop is unbreakable
RFC PATCH 1/1 e2fsprogs: dblist iteration loop is unbreakable
ext2fs_dblist_iterate breaks its iteration loop if callback's return value has set DBLIST_ABORT bit.
If ext2fs_dblist_iterate is called by ext2fs_dblist_dir_iterate, the callback is db_dir_proc->ext2fs_process_dir_block, which returns BLOCK_ABORT if something goes wrong.BLOCK_ABORT is defined as 2, whereas DBLIST_ABORT is 1.
As result ext2fs_dblist_iterate does not break the iteration loop when ext2fs_process_dir_block returns BLOCK_ABORT.
lib/ext2fs/dblist.c renamed from lib/ext2fs/dblist.c~break-dblist-loop +1 -1
@@ -232,7 +232,7 @@ errcode_t ext2fs_dblist_iterate(ext2_dblext2fs_dblist_sort (dblist,0 );for (i=0 ; i < dblist->count; i++) { ret = (*func)(dblist->fs, &dblist->list[(int )i], priv_data); -if (ret &DBLIST_ABORT ) +if ((ret &DBLIST_ABORT ) || (ret ==BLOCK_ABORT ))return 0 ; }return 0 ;
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Quoted 9 lines · Vladimir V. Saveliev
ext2fs_dblist_iteratebreaks its iteration loop if callback's return value has setDBLIST_ABORTbit.
Ifext2fs_dblist_iterateis called byext2fs_dblist_dir_iterate, the callback isdb_dir_proc->ext2fs_process_dir_block, which returnsBLOCK_ABORTif something goes wrong.BLOCK_ABORTis defined as 2, whereasDBLIST_ABORTis 1.
As resultext2fs_dblist_iteratedoes not break the iteration loop whenext2fs_process_dir_blockreturnsBLOCK_ABORT.
Hi, thanks for reporting this and sending a patch. Unfortunately there were a couple of problems with it.
First of all, please in the future remember to send your patches with a Signed-off-by: header.
Secondly, DBLIST_ABORT and BLOCK_ABORT come from different number spaces, and and so a fix like this:
Review
Quoted 2 lines
(quoted diff) +1
-0+ if ((ret & DBLIST_ABORT) || (ret == BLOCK_ABORT)) return 0;
Raises an eyebrow right away. (Also, the return convention with the BLOCK_* flags are they are a bitfield, so you always compare them with a boolean & operator: ret & BLOCK_ABORT).
The real issue is that the helper function db_dir_proc is supposed to return flags of the form DBLIST_*, so it should have never called ext2fs_process_dir_block() without translating its return codes. HOWEVER, when I tried the obvious patch which mapped the return codes:
lib/ext2fs/dblist_dir.c +6 -2
@@ -66,10 +66,14 @@ static int db_dir_proc(ext2_filsys fs, struct ext2_db_entry *db_info, void *priv_data) {struct dir_context *ctx; +int ret; ctx = (struct dir_context *) priv_data; ctx->dir = db_info->ino; -return ext2fs_process_dir_block (fs, &db_info->blk, - db_info->blockcnt,0 ,0 , priv_data); + ret =ext2fs_process_dir_block (fs, &db_info->blk, + db_info->blockcnt,0 ,0 , priv_data); +if (ret &BLOCK_ABORT ) +return DBLIST_ABORT ; +return 0 ; }
It turns out this caused the regression test suite to break. (Moral of the story: ***Always run the regression test suite, since it will catch things you might not have expected!*** Your original patch would have failed the regression test for the same reason, by which I can deduce that you didn't run "make check" as part of testing out your patch.)
The reason for the test failure is there are multiple reasons why ext2fs_process_dir_block() might return BLOCK_ABORT. It could do so because the callback function (in this case search_dirent_proc() in e2fsck/pass1b.c) has returned DIRENT_ABORT, but it can also do so because a directory block was corrupted, or there was an I/O error reading the directory block, etc., and in that case we don't want to abort the entire dblist iteration. The ultimate correct patch is attached below, and has been checked into the e2fsprogs maint branch.
- Ted
commit f6341e9c70eb4e0ded51ca96aeaa79a72222c069
Author: Theodore Ts'o <[email protected]> Date: Sun Sep 23 11:39:24 2007 -0400
ext2fs_dblist_dir_iterate: Fix ABORT propagation logic
ext2fs_dblist_dir_iterate() calls ext2fs_dblist_iterate(), which calls ext2fs_process_dir_block(), which in turn calls the helper function db_dir_proc() which calls callback function passed into ext2fs_dblist_dir_iterate(). At each stage the conventions for signalling requests to abort the iteration or to signal errors changes, db_dir_proc() was not properly mapping the abort request back to ext2fs_dblist_iterate().
Currently db_dir_proc() is ignoring errors (i/o errors or directory block corrupt errors) from ext2fs_process_dir_block(), since the main user of ext2fs_dblist_dir_iterate() is e2fsck, for which this is the correct behavior. In the future ext2fs_dblist_dir_iterate() could take a flag which would cause it to abort if ext2fs_process_dir_block() returns an error; however, it's not clear how useful this would be since we don't have a way of signalling the exact nature of which block had the error, and the caller wouldn't have a good way of knowing what percentage of the directory block list had been processed. Ultimately this may not be the best interface for applications that need that level of error reporting.
Thanks to Vladimir V. Saveliev <[email protected]> for pointing out this problem.
lib/ext2fs/dblist_dir.c +7 -2
@@ -66,10 +66,15 @@ static int db_dir_proc(ext2_filsys fs, struct ext2_db_entry *db_info, void *priv_data) {struct dir_context *ctx; +int ret; ctx = (struct dir_context *) priv_data; ctx->dir = db_info->ino; + ctx->errcode =0 ; -return ext2fs_process_dir_block (fs, &db_info->blk, - db_info->blockcnt,0 ,0 , priv_data); + ret =ext2fs_process_dir_block (fs, &db_info->blk, + db_info->blockcnt,0 ,0 , priv_data); +if ((ret &BLOCK_ABORT ) && !ctx->errcode) +return DBLIST_ABORT ; +return 0 ; }