From fb2a0010cd0f48d88405eab9e39b30fd3bfe88e2 Mon Sep 17 00:00:00 2001 From: Charan Teja Kalla Date: Fri, 19 Jun 2020 17:27:19 +0530 Subject: [PATCH] UPSTREAM: dmabuf: use spinlock to access dmabuf->name MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit [ Upstream commit 6348dd291e3653534a9e28e6917569bc9967b35b ] There exists a sleep-while-atomic bug while accessing the dmabuf->name under mutex in the dmabuffs_dname(). This is caused from the SELinux permissions checks on a process where it tries to validate the inherited files from fork() by traversing them through iterate_fd() (which traverse files under spin_lock) and call match_file(security/selinux/hooks.c) where the permission checks happen. This audit information is logged using dump_common_audit_data() where it calls d_path() to get the file path name. If the file check happen on the dmabuf's fd, then it ends up in ->dmabuffs_dname() and use mutex to access dmabuf->name. The flow will be like below: flush_unauthorized_files() iterate_fd() spin_lock() --> Start of the atomic section. match_file() file_has_perm() avc_has_perm() avc_audit() slow_avc_audit() common_lsm_audit() dump_common_audit_data() audit_log_d_path() d_path() dmabuffs_dname() mutex_lock()--> Sleep while atomic. Call trace captured (on 4.19 kernels) is below: ___might_sleep+0x204/0x208 __might_sleep+0x50/0x88 __mutex_lock_common+0x5c/0x1068 __mutex_lock_common+0x5c/0x1068 mutex_lock_nested+0x40/0x50 dmabuffs_dname+0xa0/0x170 d_path+0x84/0x290 audit_log_d_path+0x74/0x130 common_lsm_audit+0x334/0x6e8 slow_avc_audit+0xb8/0xf8 avc_has_perm+0x154/0x218 file_has_perm+0x70/0x180 match_file+0x60/0x78 iterate_fd+0x128/0x168 selinux_bprm_committing_creds+0x178/0x248 security_bprm_committing_creds+0x30/0x48 install_exec_creds+0x1c/0x68 load_elf_binary+0x3a4/0x14e0 search_binary_handler+0xb0/0x1e0 So, use spinlock to access dmabuf->name to avoid sleep-while-atomic. Cc: [5.3+] Change-Id: Ic27dbffaf36d76e1f77f47243696c99a106c6663 Signed-off-by: Charan Teja Kalla Reviewed-by: Michael J. Ruhl Acked-by: Christian König [sumits: added comment to spinlock_t definition to avoid warning] Signed-off-by: Sumit Semwal Link: https://patchwork.freedesktop.org/patch/msgid/a83e7f0d-4e54-9848-4b58-e1acdbe06735@codeaurora.org Signed-off-by: Sasha Levin --- drivers/dma-buf/dma-buf.c | 3 +++ include/linux/dma-buf.h | 2 +- 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 23583178fc65..24b242aab1dd 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -408,8 +408,10 @@ static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf) kfree(name); goto out_unlock; } + spin_lock(&dmabuf->name_lock); kfree(dmabuf->name); dmabuf->name = name; + spin_unlock(&dmabuf->name_lock); out_unlock: spin_unlock(&dmabuf->name_lock); @@ -623,6 +625,7 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info) dmabuf->size = exp_info->size; dmabuf->exp_name = exp_info->exp_name; dmabuf->owner = exp_info->owner; + spin_lock_init(&dmabuf->name_lock); init_waitqueue_head(&dmabuf->poll); dmabuf->cb_excl.poll = dmabuf->cb_shared.poll = &dmabuf->poll; dmabuf->cb_excl.active = dmabuf->cb_shared.active = 0; diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 9ed978c7a480..e898a5373510 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -449,7 +449,7 @@ struct dma_buf { void *vmap_ptr; const char *exp_name; const char *name; - spinlock_t name_lock; + spinlock_t name_lock; /* spinlock to protect name access */ #if defined(CONFIG_DEBUG_FS) ktime_t ktime; #endif