From 3dc91d4338d698ce77832985f9cb183d8eeaf6be Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Thu, 9 Jan 2014 21:46:34 -0500 Subject: SELinux: Fix possible NULL pointer dereference in selinux_inode_permission() While running stress tests on adding and deleting ftrace instances I hit this bug: BUG: unable to handle kernel NULL pointer dereference at 0000000000000020 IP: selinux_inode_permission+0x85/0x160 PGD 63681067 PUD 7ddbe067 PMD 0 Oops: 0000 [#1] PREEMPT CPU: 0 PID: 5634 Comm: ftrace-test-mki Not tainted 3.13.0-rc4-test-00033-gd2a6dde-dirty #20 Hardware name: /DG965MQ, BIOS MQ96510J.86A.0372.2006.0605.1717 06/05/2006 task: ffff880078375800 ti: ffff88007ddb0000 task.ti: ffff88007ddb0000 RIP: 0010:[] [] selinux_inode_permission+0x85/0x160 RSP: 0018:ffff88007ddb1c48 EFLAGS: 00010246 RAX: 0000000000000000 RBX: 0000000000800000 RCX: ffff88006dd43840 RDX: 0000000000000001 RSI: 0000000000000081 RDI: ffff88006ee46000 RBP: ffff88007ddb1c88 R08: 0000000000000000 R09: ffff88007ddb1c54 R10: 6e6576652f6f6f66 R11: 0000000000000003 R12: 0000000000000000 R13: 0000000000000081 R14: ffff88006ee46000 R15: 0000000000000000 FS: 00007f217b5b6700(0000) GS:ffffffff81e21000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033^M CR2: 0000000000000020 CR3: 000000006a0fe000 CR4: 00000000000007f0 Call Trace: security_inode_permission+0x1c/0x30 __inode_permission+0x41/0xa0 inode_permission+0x18/0x50 link_path_walk+0x66/0x920 path_openat+0xa6/0x6c0 do_filp_open+0x43/0xa0 do_sys_open+0x146/0x240 SyS_open+0x1e/0x20 system_call_fastpath+0x16/0x1b Code: 84 a1 00 00 00 81 e3 00 20 00 00 89 d8 83 c8 02 40 f6 c6 04 0f 45 d8 40 f6 c6 08 74 71 80 cf 02 49 8b 46 38 4c 8d 4d cc 45 31 c0 <0f> b7 50 20 8b 70 1c 48 8b 41 70 89 d9 8b 78 04 e8 36 cf ff ff RIP selinux_inode_permission+0x85/0x160 CR2: 0000000000000020 Investigating, I found that the inode->i_security was NULL, and the dereference of it caused the oops. in selinux_inode_permission(): isec = inode->i_security; rc = avc_has_perm_noaudit(sid, isec->sid, isec->sclass, perms, 0, &avd); Note, the crash came from stressing the deletion and reading of debugfs files. I was not able to recreate this via normal files. But I'm not sure they are safe. It may just be that the race window is much harder to hit. What seems to have happened (and what I have traced), is the file is being opened at the same time the file or directory is being deleted. As the dentry and inode locks are not held during the path walk, nor is the inodes ref counts being incremented, there is nothing saving these structures from being discarded except for an rcu_read_lock(). The rcu_read_lock() protects against freeing of the inode, but it does not protect freeing of the inode_security_struct. Now if the freeing of the i_security happens with a call_rcu(), and the i_security field of the inode is not changed (it gets freed as the inode gets freed) then there will be no issue here. (Linus Torvalds suggested not setting the field to NULL such that we do not need to check if it is NULL in the permission check). Note, this is a hack, but it fixes the problem at hand. A real fix is to restructure the destroy_inode() to call all the destructor handlers from the RCU callback. But that is a major job to do, and requires a lot of work. For now, we just band-aid this bug with this fix (it works), and work on a more maintainable solution in the future. Link: http://lkml.kernel.org/r/20140109101932.0508dec7@gandalf.local.home Link: http://lkml.kernel.org/r/20140109182756.17abaaa8@gandalf.local.home Cc: stable@vger.kernel.org Signed-off-by: Steven Rostedt Signed-off-by: Linus Torvalds --- security/selinux/hooks.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) (limited to 'security/selinux/hooks.c') diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 6625699f497c..57b0b49f4e6e 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -234,6 +234,14 @@ static int inode_alloc_security(struct inode *inode) return 0; } +static void inode_free_rcu(struct rcu_head *head) +{ + struct inode_security_struct *isec; + + isec = container_of(head, struct inode_security_struct, rcu); + kmem_cache_free(sel_inode_cache, isec); +} + static void inode_free_security(struct inode *inode) { struct inode_security_struct *isec = inode->i_security; @@ -244,8 +252,16 @@ static void inode_free_security(struct inode *inode) list_del_init(&isec->list); spin_unlock(&sbsec->isec_lock); - inode->i_security = NULL; - kmem_cache_free(sel_inode_cache, isec); + /* + * The inode may still be referenced in a path walk and + * a call to selinux_inode_permission() can be made + * after inode_free_security() is called. Ideally, the VFS + * wouldn't do this, but fixing that is a much harder + * job. For now, simply free the i_security via RCU, and + * leave the current inode->i_security pointer intact. + * The inode will be freed after the RCU grace period too. + */ + call_rcu(&isec->rcu, inode_free_rcu); } static int file_alloc_security(struct file *file) -- cgit v1.2.1 From 52a4c6404f91f2d2c5592ee6365a8418c4565f53 Mon Sep 17 00:00:00 2001 From: Nikolay Aleksandrov Date: Fri, 7 Mar 2014 12:44:19 +0100 Subject: selinux: add gfp argument to security_xfrm_policy_alloc and fix callers security_xfrm_policy_alloc can be called in atomic context so the allocation should be done with GFP_ATOMIC. Add an argument to let the callers choose the appropriate way. In order to do so a gfp argument needs to be added to the method xfrm_policy_alloc_security in struct security_operations and to the internal function selinux_xfrm_alloc_user. After that switch to GFP_ATOMIC in the atomic callers and leave GFP_KERNEL as before for the rest. The path that needed the gfp argument addition is: security_xfrm_policy_alloc -> security_ops.xfrm_policy_alloc_security -> all users of xfrm_policy_alloc_security (e.g. selinux_xfrm_policy_alloc) -> selinux_xfrm_alloc_user (here the allocation used to be GFP_KERNEL only) Now adding a gfp argument to selinux_xfrm_alloc_user requires us to also add it to security_context_to_sid which is used inside and prior to this patch did only GFP_KERNEL allocation. So add gfp argument to security_context_to_sid and adjust all of its callers as well. CC: Paul Moore CC: Dave Jones CC: Steffen Klassert CC: Fan Du CC: David S. Miller CC: LSM list CC: SELinux list Signed-off-by: Nikolay Aleksandrov Acked-by: Paul Moore Signed-off-by: Steffen Klassert --- security/selinux/hooks.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) (limited to 'security/selinux/hooks.c') diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 4b34847208cc..b332e2cc0954 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -668,7 +668,7 @@ static int selinux_set_mnt_opts(struct super_block *sb, if (flags[i] == SBLABEL_MNT) continue; rc = security_context_to_sid(mount_options[i], - strlen(mount_options[i]), &sid); + strlen(mount_options[i]), &sid, GFP_KERNEL); if (rc) { printk(KERN_WARNING "SELinux: security_context_to_sid" "(%s) failed for (dev %s, type %s) errno=%d\n", @@ -2489,7 +2489,8 @@ static int selinux_sb_remount(struct super_block *sb, void *data) if (flags[i] == SBLABEL_MNT) continue; len = strlen(mount_options[i]); - rc = security_context_to_sid(mount_options[i], len, &sid); + rc = security_context_to_sid(mount_options[i], len, &sid, + GFP_KERNEL); if (rc) { printk(KERN_WARNING "SELinux: security_context_to_sid" "(%s) failed for (dev %s, type %s) errno=%d\n", @@ -2893,7 +2894,7 @@ static int selinux_inode_setxattr(struct dentry *dentry, const char *name, if (rc) return rc; - rc = security_context_to_sid(value, size, &newsid); + rc = security_context_to_sid(value, size, &newsid, GFP_KERNEL); if (rc == -EINVAL) { if (!capable(CAP_MAC_ADMIN)) { struct audit_buffer *ab; @@ -3050,7 +3051,7 @@ static int selinux_inode_setsecurity(struct inode *inode, const char *name, if (!value || !size) return -EACCES; - rc = security_context_to_sid((void *)value, size, &newsid); + rc = security_context_to_sid((void *)value, size, &newsid, GFP_KERNEL); if (rc) return rc; @@ -5529,7 +5530,7 @@ static int selinux_setprocattr(struct task_struct *p, str[size-1] = 0; size--; } - error = security_context_to_sid(value, size, &sid); + error = security_context_to_sid(value, size, &sid, GFP_KERNEL); if (error == -EINVAL && !strcmp(name, "fscreate")) { if (!capable(CAP_MAC_ADMIN)) { struct audit_buffer *ab; @@ -5638,7 +5639,7 @@ static int selinux_secid_to_secctx(u32 secid, char **secdata, u32 *seclen) static int selinux_secctx_to_secid(const char *secdata, u32 seclen, u32 *secid) { - return security_context_to_sid(secdata, seclen, secid); + return security_context_to_sid(secdata, seclen, secid, GFP_KERNEL); } static void selinux_release_secctx(char *secdata, u32 seclen) -- cgit v1.2.1