Hi I'm submitting this patch for 2.6.30 merge window. FAT filesystem used down_read(&mapping->host->i_alloc_sem) to prevent a race between bmap and truncate. However, such race is present in all the other filesystems --- it is generally assumed that blocks queried with get_block won't disappear while get_block is in progress. The race can be only triggered by root, non-privileged users can't use bmap, so it is not a security issue (unless there is some program run by root that bmaps users' files). This patch fixes the race in a generic way, in all the filesystems. If some filesystem employs its own locking and doesn't want to take i_alloc_sem (I don't know about any, where taking i_alloc_sem could be problem), let it use its own function and not generic_block_bmap. Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx> --- fs/buffer.c | 8 ++++++++ fs/fat/inode.c | 2 -- 2 files changed, 8 insertions(+), 2 deletions(-) Index: linux-2.6.29-devel/fs/buffer.c =================================================================== --- linux-2.6.29-devel.orig/fs/buffer.c 2009-03-29 04:48:38.000000000 +0200 +++ linux-2.6.29-devel/fs/buffer.c 2009-03-29 05:26:53.000000000 +0200 @@ -2963,7 +2963,15 @@ sector_t generic_block_bmap(struct addre tmp.b_state = 0; tmp.b_blocknr = 0; tmp.b_size = 1 << inode->i_blkbits; + + /* + * Protect the inode from being truncated while get_block is + * in progress. + */ + down_read(&mapping->host->i_alloc_sem); get_block(inode, block, &tmp, 0); + up_read(&mapping->host->i_alloc_sem); + return tmp.b_blocknr; } Index: linux-2.6.29-devel/fs/fat/inode.c =================================================================== --- linux-2.6.29-devel.orig/fs/fat/inode.c 2009-03-29 04:46:35.000000000 +0200 +++ linux-2.6.29-devel/fs/fat/inode.c 2009-03-29 05:26:53.000000000 +0200 @@ -202,9 +202,7 @@ static sector_t _fat_bmap(struct address sector_t blocknr; /* fat_get_cluster() assumes the requested blocknr isn't truncated. */ - down_read(&mapping->host->i_alloc_sem); blocknr = generic_block_bmap(mapping, block, fat_get_block); - up_read(&mapping->host->i_alloc_sem); return blocknr; } -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
