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@xxxxxxxxxxxxxxx> [5.3+]
Signed-off-by: Charan Teja Reddy <charante@xxxxxxxxxxxxxx>
---
Changes in V2: Addressed review comments from Ruhl, Michael J
Changes in V1: https://lore.kernel.org/patchwork/patch/1255055/
drivers/dma-buf/dma-buf.c | 11 +++++++----
include/linux/dma-buf.h | 1 +
2 files changed, 8 insertions(+), 4 deletions(-)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 01ce125..d81d298 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);
return dynamic_dname(dentry, buffer, buflen, "/%s:%s",
dentry->d_name.name, ret > 0 ? name : "");
@@ -341,8 +341,10 @@ 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:
dma_resv_unlock(dmabuf->resv);
@@ -405,10 +407,10 @@ 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 +548,7 @@ 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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