-----Original Message----- From: dri-devel dri-devel-bounces@lists.freedesktop.org On Behalf Of Ruhl, Michael J Sent: Tuesday, June 16, 2020 9:51 AM To: Charan Teja Kalla charante@codeaurora.org; Sumit Semwal sumit.semwal@linaro.org; open list:DMA BUFFER SHARING FRAMEWORK linux-media@vger.kernel.org; DRI mailing list <dri- devel@lists.freedesktop.org> Cc: Linaro MM SIG linaro-mm-sig@lists.linaro.org; vinmenon@codeaurora.org; LKML linux-kernel@vger.kernel.org; stable@vger.kernel.org Subject: RE: [PATCH] dmabuf: use spinlock to access dmabuf->name
-----Original Message----- From: dri-devel dri-devel-bounces@lists.freedesktop.org On Behalf Of Charan Teja Kalla Sent: Thursday, June 11, 2020 9:40 AM To: Sumit Semwal sumit.semwal@linaro.org; open list:DMA BUFFER SHARING FRAMEWORK linux-media@vger.kernel.org; DRI mailing list <dri- devel@lists.freedesktop.org> Cc: Linaro MM SIG linaro-mm-sig@lists.linaro.org; vinmenon@codeaurora.org; LKML linux-kernel@vger.kernel.org; stable@vger.kernel.org Subject: [PATCH] dmabuf: use spinlock to access dmabuf->name
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: stable@vger.kernel.org [5.3+] Signed-off-by: Charan Teja Reddy charante@codeaurora.org
drivers/dma-buf/dma-buf.c | 13 +++++++------ include/linux/dma-buf.h | 1 + 2 files changed, 8 insertions(+), 6 deletions(-)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 01ce125..2e0456c 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -45,10 +45,10 @@ static char *dmabuffs_dname(struct dentry *dentry, char *buffer, int buflen) size_t ret = 0;
dmabuf = dentry->d_fsdata;
- dma_resv_lock(dmabuf->resv, NULL);
- spin_lock(&dmabuf->name_lock); if (dmabuf->name) ret = strlcpy(name, dmabuf->name, DMA_BUF_NAME_LEN);
- dma_resv_unlock(dmabuf->resv);
- spin_unlock(&dmabuf->name_lock);
I am not really clear on why you need this lock.
If name == NULL you have no issues. If name is real, you have no issues.
If name is freed you will copy garbage, but the only way for that to happen is that _set_name or _release have to be called at just the right time.
And the above would probably only be an issue if the set_name was called, so you will get NULL or a real name.
Is there a reason for the lock here?
Mike
Maybe dmabuf->name = NULL after the kfree(dmabuf->name) in:
dma_buf_release()
Would be sufficient?
M
return dynamic_dname(dentry, buffer, buflen, "/%s:%s", dentry->d_name.name, ret > 0 ? name : ""); @@ -335,7 +335,7 @@ static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf) if (IS_ERR(name)) return PTR_ERR(name);
- dma_resv_lock(dmabuf->resv, NULL);
- spin_lock(&dmabuf->name_lock); if (!list_empty(&dmabuf->attachments)) { ret = -EBUSY; kfree(name);
@@ -345,7 +345,7 @@ static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf) dmabuf->name = name;
out_unlock:
- dma_resv_unlock(dmabuf->resv);
- spin_unlock(&dmabuf->name_lock); return ret;
}
@@ -405,10 +405,10 @@ static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file) /* Don't count the temporary reference taken inside procfs seq_show */ seq_printf(m, "count:\t%ld\n", file_count(dmabuf->file) - 1); seq_printf(m, "exp_name:\t%s\n", dmabuf->exp_name);
- dma_resv_lock(dmabuf->resv, NULL);
- spin_lock(&dmabuf->name_lock); if (dmabuf->name) seq_printf(m, "name:\t%s\n", dmabuf->name);
- dma_resv_unlock(dmabuf->resv);
- spin_unlock(&dmabuf->name_lock);
}
static const struct file_operations dma_buf_fops = { @@ -546,6 +546,7 @@ 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 ab0c156..93108fd 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -311,6 +311,7 @@ struct dma_buf { void *vmap_ptr; const char *exp_name; const char *name;
- spinlock_t name_lock; struct module *owner; struct list_head list_node; void *priv;
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