From 2a9b8cba62c0741109c33a2be700ff3d7703a7c2 Mon Sep 17 00:00:00 2001 From: Roman Pen Date: Sun, 8 Jan 2017 20:59:35 -0500 Subject: [PATCH] ext4: Include forgotten start block on fallocate insert range While doing 'insert range' start block should be also shifted right. The bug can be easily reproduced by the following test: ptr = malloc(4096); assert(ptr); fd = open("./ext4.file", O_CREAT | O_TRUNC | O_RDWR, 0600); assert(fd >= 0); rc = fallocate(fd, 0, 0, 8192); assert(rc == 0); for (i = 0; i < 2048; i++) *((unsigned short *)ptr + i) = 0xbeef; rc = pwrite(fd, ptr, 4096, 0); assert(rc == 4096); rc = pwrite(fd, ptr, 4096, 4096); assert(rc == 4096); for (block = 2; block < 1000; block++) { rc = fallocate(fd, FALLOC_FL_INSERT_RANGE, 4096, 4096); assert(rc == 0); for (i = 0; i < 2048; i++) *((unsigned short *)ptr + i) = block; rc = pwrite(fd, ptr, 4096, 4096); assert(rc == 4096); } Because start block is not included in the range the hole appears at the wrong offset (just after the desired offset) and the following pwrite() overwrites already existent block, keeping hole untouched. Simple way to verify wrong behaviour is to check zeroed blocks after the test: $ hexdump ./ext4.file | grep '0000 0000' The root cause of the bug is a wrong range (start, stop], where start should be inclusive, i.e. [start, stop]. This patch fixes the problem by including start into the range. But not to break left shift (range collapse) stop points to the beginning of the a block, not to the end. The other not obvious change is an iterator check on validness in a main loop. Because iterator is unsigned the following corner case should be considered with care: insert a block at 0 offset, when stop variables overflows and never becomes less than start, which is 0. To handle this special case iterator is set to NULL to indicate that end of the loop is reached. Fixes: 331573febb6a2 Signed-off-by: Roman Pen Signed-off-by: Theodore Ts'o Cc: Namjae Jeon Cc: Andreas Dilger Cc: stable@vger.kernel.org --- fs/ext4/extents.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c index 3e295d3350a9..4d3014b5a3f9 100644 --- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -5343,8 +5343,7 @@ ext4_ext_shift_extents(struct inode *inode, handle_t *handle, if (!extent) goto out; - stop = le32_to_cpu(extent->ee_block) + - ext4_ext_get_actual_len(extent); + stop = le32_to_cpu(extent->ee_block); /* * In case of left shift, Don't start shifting extents until we make @@ -5383,8 +5382,12 @@ ext4_ext_shift_extents(struct inode *inode, handle_t *handle, else iterator = &stop; - /* Its safe to start updating extents */ - while (start < stop) { + /* + * Its safe to start updating extents. Start and stop are unsigned, so + * in case of right shift if extent with 0 block is reached, iterator + * becomes NULL to indicate the end of the loop. + */ + while (iterator && start <= stop) { path = ext4_find_extent(inode, *iterator, &path, 0); if (IS_ERR(path)) return PTR_ERR(path); @@ -5412,8 +5415,11 @@ ext4_ext_shift_extents(struct inode *inode, handle_t *handle, ext4_ext_get_actual_len(extent); } else { extent = EXT_FIRST_EXTENT(path[depth].p_hdr); - *iterator = le32_to_cpu(extent->ee_block) > 0 ? - le32_to_cpu(extent->ee_block) - 1 : 0; + if (le32_to_cpu(extent->ee_block) > 0) + *iterator = le32_to_cpu(extent->ee_block) - 1; + else + /* Beginning is reached, end of the loop */ + iterator = NULL; /* Update path extent in case we need to stop */ while (le32_to_cpu(extent->ee_block) < start) extent++;