CVE-2024-26870

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

NFSv4.2: fix nfs4_listxattr kernel BUG at mm/usercopy.c:102

A call to listxattr() with a buffer size = 0 returns the actual

size of the buffer needed for a subsequent call. When size > 0,

nfs4_listxattr() does not return an error because either

generic_listxattr() or nfs4_listxattr_nfs4_label() consumes

exactly all the bytes then size is 0 when calling

nfs4_listxattr_nfs4_user() which then triggers the following

kernel BUG:

[ 99.403778] kernel BUG at mm/usercopy.c:102!

[ 99.404063] Internal error: Oops - BUG: 00000000f2000800 [#1] SMP

[ 99.408463] CPU: 0 PID: 3310 Comm: python3 Not tainted 6.6.0-61.fc40.aarch64 #1

[ 99.415827] Call trace:

[ 99.415985] usercopy_abort+0x70/0xa0

[ 99.416227] __check_heap_object+0x134/0x158

[ 99.416505] check_heap_object+0x150/0x188

[ 99.416696] __check_object_size.part.0+0x78/0x168

[ 99.416886] __check_object_size+0x28/0x40

[ 99.417078] listxattr+0x8c/0x120

[ 99.417252] path_listxattr+0x78/0xe0

[ 99.417476] __arm64_sys_listxattr+0x28/0x40

[ 99.417723] invoke_syscall+0x78/0x100

[ 99.417929] el0_svc_common.constprop.0+0x48/0xf0

[ 99.418186] do_el0_svc+0x24/0x38

[ 99.418376] el0_svc+0x3c/0x110

[ 99.418554] el0t_64_sync_handler+0x120/0x130

[ 99.418788] el0t_64_sync+0x194/0x198

[ 99.418994] Code: aa0003e3 d000a3e0 91310000 97f49bdb (d4210000)

Issue is reproduced when generic_listxattr() returns 'system.nfs4_acl',

thus calling lisxattr() with size = 16 will trigger the bug.

Add check on nfs4_listxattr() to return ERANGE error when it is

called with size > 0 and the return value is greater than size.