Created attachment 174961 [details]
btrfs-image causing write/read access to unallocated memory

Running btrfs-progs v3.19.1

The btrfs-image attached to this bug causes the btrfs-userland tool to overflow some data structures, leading to unallocated memory being written to and read from. A segfault results shortly after. Reproduced on x86-64 and i686.

The kernel seems to be less affected and fails to mount the image. I didn't investigate whether the reads/writes could be used to gain control over $EIP. Since the first invalid write of 8 bytes seems to run into adjacent heap blocks (crash in unlink()), it may be possible though.

gdb output:

Program received signal SIGSEGV, Segmentation fault.
malloc_consolidate (av=av@entry=0x32629b7cc0 <main_arena>) at malloc.c:4151
4151		    unlink(av, p, bck, fwd);
(gdb) bt
#0  malloc_consolidate (av=av@entry=0x32629b7cc0 <main_arena>) at malloc.c:4151
#1  0x0000003262680628 in _int_malloc (av=av@entry=0x32629b7cc0 <main_arena>, bytes=bytes@entry=4224) at malloc.c:3420
#2  0x000000326268315e in __GI___libc_malloc (bytes=4224) at malloc.c:2896
#3  0x0000000000449d15 in __alloc_extent_buffer (tree=0x88c078, bytenr=4288512, blocksize=4096) at extent_io.c:541
#4  0x000000000044a8b4 in alloc_extent_buffer (tree=0x88c078, bytenr=4288512, blocksize=4096) at extent_io.c:648
#5  0x000000000043b1a0 in btrfs_find_create_tree_block (root=root@entry=0x895840, bytenr=<optimized out>, 
    blocksize=<optimized out>) at disk-io.c:159
#6  0x000000000043ca4e in read_tree_block (root=root@entry=0x895840, bytenr=<optimized out>, blocksize=<optimized out>, 
    parent_transid=13) at disk-io.c:287
#7  0x000000000043ccb7 in find_and_setup_root (tree_root=0x88c250, fs_info=<optimized out>, objectid=5, root=0x895840)
    at disk-io.c:557
#8  0x000000000043ce92 in btrfs_read_fs_root_no_cache (fs_info=fs_info@entry=0x88c010, location=location@entry=0x7fffffffd960)
    at disk-io.c:640
#9  0x000000000043d060 in btrfs_read_fs_root (fs_info=fs_info@entry=0x88c010, location=location@entry=0x7fffffffd960)
    at disk-io.c:739
#10 0x000000000043d48c in btrfs_setup_all_roots (fs_info=fs_info@entry=0x88c010, root_tree_bytenr=<optimized out>, 
    root_tree_bytenr@entry=0, flags=flags@entry=OPEN_CTREE_EXCLUSIVE) at disk-io.c:988
#11 0x000000000043d802 in __open_ctree_fd (fp=fp@entry=3, path=path@entry=0x7fffffffe20d "ramdisk/btrfs_fukked.bin", 
    sb_bytenr=65536, sb_bytenr@entry=0, root_tree_bytenr=root_tree_bytenr@entry=0, flags=flags@entry=OPEN_CTREE_EXCLUSIVE)
    at disk-io.c:1199
#12 0x000000000043d965 in open_ctree_fs_info (filename=0x7fffffffe20d "ramdisk/btrfs_fukked.bin", sb_bytenr=sb_bytenr@entry=0, 
    root_tree_bytenr=root_tree_bytenr@entry=0, flags=flags@entry=OPEN_CTREE_EXCLUSIVE) at disk-io.c:1231
#13 0x0000000000427bf5 in cmd_check (argc=1, argv=0x7fffffffdea0) at cmds-check.c:9326
#14 0x000000000040e5a2 in main (argc=2, argv=0x7fffffffdea0) at btrfs.c:245


valgrind output:

==32463== Memcheck, a memory error detector
==32463== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==32463== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==32463== Command: btrfs check ramdisk/btrfs_fukked.bin
==32463== 
==32463== Invalid write of size 8
==32463==    at 0x4386FB: btrfs_search_slot (ctree.c:1119)
==32463==    by 0x4427F7: UnknownInlinedFun (extent-tree.c:3117)
==32463==    by 0x4427F7: btrfs_read_block_groups (extent-tree.c:3167)
==32463==    by 0x43D4F2: btrfs_setup_all_roots (disk-io.c:983)
==32463==    by 0x43D801: __open_ctree_fd (disk-io.c:1199)
==32463==    by 0x43D964: open_ctree_fs_info (disk-io.c:1231)
==32463==    by 0x427BF4: cmd_check (cmds-check.c:9326)
==32463==    by 0x40E5A1: main (btrfs.c:245)
==32463==  Address 0x4c409f0 is 16 bytes after a block of size 144 alloc'd
==32463==    at 0x4A08946: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==32463==    by 0x4427AB: btrfs_read_block_groups (extent-tree.c:3162)
==32463==    by 0x43D4F2: btrfs_setup_all_roots (disk-io.c:983)
==32463==    by 0x43D801: __open_ctree_fd (disk-io.c:1199)
==32463==    by 0x43D964: open_ctree_fs_info (disk-io.c:1231)
==32463==    by 0x427BF4: cmd_check (cmds-check.c:9326)
==32463==    by 0x40E5A1: main (btrfs.c:245)
==32463== 
==32463== Invalid read of size 8
==32463==    at 0x436E70: check_block.part.14 (ctree.c:548)
==32463==    by 0x438954: UnknownInlinedFun (kerncompat.h:91)
==32463==    by 0x438954: btrfs_search_slot (ctree.c:1120)
==32463==    by 0x4427F7: UnknownInlinedFun (extent-tree.c:3117)
==32463==    by 0x4427F7: btrfs_read_block_groups (extent-tree.c:3167)
==32463==    by 0x43D4F2: btrfs_setup_all_roots (disk-io.c:983)
==32463==    by 0x43D801: __open_ctree_fd (disk-io.c:1199)
==32463==    by 0x43D964: open_ctree_fs_info (disk-io.c:1231)
==32463==    by 0x427BF4: cmd_check (cmds-check.c:9326)
==32463==    by 0x40E5A1: main (btrfs.c:245)
==32463==  Address 0x4c409f8 is 24 bytes after a block of size 144 in arena "client"
==32463== 
==32463== Invalid read of size 4
==32463==    at 0x436E84: UnknownInlinedFun (ctree.h:1605)
==32463==    by 0x436E84: UnknownInlinedFun (ctree.h:1612)
==32463==    by 0x436E84: check_block.part.14 (ctree.c:550)
==32463==    by 0x438954: UnknownInlinedFun (kerncompat.h:91)
==32463==    by 0x438954: btrfs_search_slot (ctree.c:1120)
==32463==    by 0x4427F7: UnknownInlinedFun (extent-tree.c:3117)
==32463==    by 0x4427F7: btrfs_read_block_groups (extent-tree.c:3167)
==32463==    by 0x43D4F2: btrfs_setup_all_roots (disk-io.c:983)
==32463==    by 0x43D801: __open_ctree_fd (disk-io.c:1199)
==32463==    by 0x43D964: open_ctree_fs_info (disk-io.c:1231)
==32463==    by 0x427BF4: cmd_check (cmds-check.c:9326)
==32463==    by 0x40E5A1: main (btrfs.c:245)
==32463==  Address 0x4c409e4 is 4 bytes after a block of size 144 alloc'd
==32463==    at 0x4A08946: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==32463==    by 0x4427AB: btrfs_read_block_groups (extent-tree.c:3162)
==32463==    by 0x43D4F2: btrfs_setup_all_roots (disk-io.c:983)
==32463==    by 0x43D801: __open_ctree_fd (disk-io.c:1199)
==32463==    by 0x43D964: open_ctree_fs_info (disk-io.c:1231)
==32463==    by 0x427BF4: cmd_check (cmds-check.c:9326)
==32463==    by 0x40E5A1: main (btrfs.c:245)
==32463== 
==32463== Invalid read of size 1
==32463==    at 0x4A0B3A0: memcpy@@GLIBC_2.14 (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==32463==    by 0x436E99: UnknownInlinedFun (ctree.h:1613)
==32463==    by 0x436E99: check_block.part.14 (ctree.c:550)
==32463==    by 0x438954: UnknownInlinedFun (kerncompat.h:91)
==32463==    by 0x438954: btrfs_search_slot (ctree.c:1120)
==32463==    by 0x4427F7: UnknownInlinedFun (extent-tree.c:3117)
==32463==    by 0x4427F7: btrfs_read_block_groups (extent-tree.c:3167)
==32463==    by 0x43D4F2: btrfs_setup_all_roots (disk-io.c:983)
==32463==    by 0x43D801: __open_ctree_fd (disk-io.c:1199)
==32463==    by 0x43D964: open_ctree_fs_info (disk-io.c:1231)
==32463==    by 0x427BF4: cmd_check (cmds-check.c:9326)
==32463==    by 0x40E5A1: main (btrfs.c:245)
==32463==  Address 0x1b1 is not stack'd, malloc'd or (recently) free'd
==32463== 
==32463== 
==32463== Process terminating with default action of signal 11 (SIGSEGV)
==32463==  Access not within mapped region at address 0x1B1
==32463==    at 0x4A0B3A0: memcpy@@GLIBC_2.14 (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==32463==    by 0x436E99: UnknownInlinedFun (ctree.h:1613)
==32463==    by 0x436E99: check_block.part.14 (ctree.c:550)
==32463==    by 0x438954: UnknownInlinedFun (kerncompat.h:91)
==32463==    by 0x438954: btrfs_search_slot (ctree.c:1120)
==32463==    by 0x4427F7: UnknownInlinedFun (extent-tree.c:3117)
==32463==    by 0x4427F7: btrfs_read_block_groups (extent-tree.c:3167)
==32463==    by 0x43D4F2: btrfs_setup_all_roots (disk-io.c:983)
==32463==    by 0x43D801: __open_ctree_fd (disk-io.c:1199)
==32463==    by 0x43D964: open_ctree_fs_info (disk-io.c:1231)
==32463==    by 0x427BF4: cmd_check (cmds-check.c:9326)
==32463==    by 0x40E5A1: main (btrfs.c:245)