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, nfs4listxattr() does not return an error because either genericlistxattr() or nfs4listxattrnfs4label() consumes exactly all the bytes then size is 0 when calling nfs4listxattrnfs4user() 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] usercopyabort+0x70/0xa0 [ 99.416227] _checkheapobject+0x134/0x158 [ 99.416505] checkheapobject+0x150/0x188 [ 99.416696] _checkobjectsize.part.0+0x78/0x168 [ 99.416886] _checkobjectsize+0x28/0x40 [ 99.417078] listxattr+0x8c/0x120 [ 99.417252] pathlistxattr+0x78/0xe0 [ 99.417476] _arm64syslistxattr+0x28/0x40 [ 99.417723] invokesyscall+0x78/0x100 [ 99.417929] el0svccommon.constprop.0+0x48/0xf0 [ 99.418186] doel0svc+0x24/0x38 [ 99.418376] el0svc+0x3c/0x110 [ 99.418554] el0t64synchandler+0x120/0x130 [ 99.418788] el0t64_sync+0x194/0x198 [ 99.418994] Code: aa0003e3 d000a3e0 91310000 97f49bdb (d4210000)

Issue is reproduced when genericlistxattr() returns 'system.nfs4acl', 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.