CVE-2024-35849

In the Linux kernel, the following vulnerability has been resolved:

btrfs: fix information leak in btrfsioctllogicaltoino()

Syzbot reported the following information leak for in btrfsioctllogicaltoino():

BUG: KMSAN: kernel-infoleak in instrumentcopytouser include/linux/instrumented.h:114 [inline] BUG: KMSAN: kernel-infoleak in _copytouser+0xbc/0x110 lib/usercopy.c:40 instrumentcopytouser include/linux/instrumented.h:114 [inline] copytouser+0xbc/0x110 lib/usercopy.c:40 copytouser include/linux/uaccess.h:191 [inline] btrfsioctllogicaltoino+0x440/0x750 fs/btrfs/ioctl.c:3499 btrfsioctl+0x714/0x1260 vfsioctl fs/ioctl.c:51 [inline] _dosysioctl fs/ioctl.c:904 [inline] _sesysioctl+0x261/0x450 fs/ioctl.c:890 _x64sysioctl+0x96/0xe0 fs/ioctl.c:890 x64syscall+0x1883/0x3b50 arch/x86/include/generated/asm/syscalls64.h:17 dosyscallx64 arch/x86/entry/common.c:52 [inline] dosyscall64+0xcf/0x1e0 arch/x86/entry/common.c:83 entrySYSCALL64after_hwframe+0x77/0x7f

Uninit was created at: _kmalloclargenode+0x231/0x370 mm/slub.c:3921 _dokmallocnode mm/slub.c:3954 [inline] _kmallocnode+0xb07/0x1060 mm/slub.c:3973 kmallocnode include/linux/slab.h:648 [inline] kvmallocnode+0xc0/0x2d0 mm/util.c:634 kvmalloc include/linux/slab.h:766 [inline] initdatacontainer+0x49/0x1e0 fs/btrfs/backref.c:2779 btrfsioctllogicaltoino+0x17c/0x750 fs/btrfs/ioctl.c:3480 btrfsioctl+0x714/0x1260 vfsioctl fs/ioctl.c:51 [inline] _dosysioctl fs/ioctl.c:904 [inline] _sesysioctl+0x261/0x450 fs/ioctl.c:890 _x64sysioctl+0x96/0xe0 fs/ioctl.c:890 x64syscall+0x1883/0x3b50 arch/x86/include/generated/asm/syscalls64.h:17 dosyscallx64 arch/x86/entry/common.c:52 [inline] dosyscall64+0xcf/0x1e0 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+0x77/0x7f

Bytes 40-65535 of 65536 are uninitialized Memory access of size 65536 starts at ffff888045a40000

This happens, because we're copying a 'struct btrfsdatacontainer' back to user-space. This btrfsdatacontainer is allocated in 'initdatacontainer()' via kvmalloc(), which does not zero-fill the memory.

Fix this by using kvzalloc() which zeroes out the memory on allocation.