Without this change, we will write data past the end of the mmp buf. Valgrind catches this: ==6373== Syscall param write(buf) points to unaddressable byte(s) ==6373== at 0x362260E470: __write_nocancel (in /lib64/libpthread-2.12.2.so) ==6373== by 0x41CF83: raw_write_blk (unix_io.c:255) ==6373== by 0x41D2BC: unix_write_blk64 (unix_io.c:757) ==6373== by 0x41A05D: ext2fs_mmp_write (mmp.c:130) ==6373== by 0x40B0C9: do_set_mmp_value (set_fields.c:806) ==6373== by 0x421B61: really_execute_command (execute_cmd.c:108) ==6373== by 0x421C54: ss_execute_line (execute_cmd.c:234) ==6373== by 0x403743: main (debugfs.c:2339) ==6373== Address 0x63f000 is not stack'd, malloc'd or (recently) free'd and in my testing it led to silent failures while writing the mmp block in debugfs: write(3, "xV4\22PMM\342\325V\274N\0\0\0\0host.name."..., 4096) = -1 EFAULT (Bad address) Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx> --- p.s. I could do with a comment about what a negative "count" means...? diff --git a/lib/ext2fs/mmp.c b/lib/ext2fs/mmp.c index 91f4fb2..b27d9a4 100644 --- a/lib/ext2fs/mmp.c +++ b/lib/ext2fs/mmp.c @@ -127,7 +127,7 @@ errcode_t ext2fs_mmp_write(ext2_filsys fs, blk64_t mmp_blk, void *buf) /* I was tempted to make this use O_DIRECT and the mmp_fd, but * this caused no end of grief, while leaving it as-is works. */ - retval = io_channel_write_blk64(fs->io, mmp_blk, -fs->blocksize, buf); + retval = io_channel_write_blk64(fs->io, mmp_blk, -(int)sizeof(struct mmp_struct), buf); #ifdef WORDS_BIGENDIAN ext2fs_swap_mmp(mmp_s); -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
