From 4ab59c3c638c6c8952bf07739805d20eb6358a4d Mon Sep 17 00:00:00 2001 From: Sumit Semwal Date: Thu, 11 Jun 2020 17:14:18 +0530 Subject: dma-buf: Move dma_buf_release() from fops to dentry_ops Charan Teja reported a 'use-after-free' in dmabuffs_dname [1], which happens if the dma_buf_release() is called while the userspace is accessing the dma_buf pseudo fs's dmabuffs_dname() in another process, and dma_buf_release() releases the dmabuf object when the last reference to the struct file goes away. I discussed with Arnd Bergmann, and he suggested that rather than tying the dma_buf_release() to the file_operations' release(), we can tie it to the dentry_operations' d_release(), which will be called when the last ref to the dentry is removed. The path exercised by __fput() calls f_op->release() first, and then calls dput, which eventually calls d_op->d_release(). In the 'normal' case, when no userspace access is happening via dma_buf pseudo fs, there should be exactly one fd, file, dentry and inode, so closing the fd will kill of everything right away. In the presented case, the dentry's d_release() will be called only when the dentry's last ref is released. Therefore, lets move dma_buf_release() from fops->release() to d_ops->d_release() Many thanks to Arnd for his FS insights :) [1]: https://lore.kernel.org/patchwork/patch/1238278/ Fixes: bb2bb9030425 ("dma-buf: add DMA_BUF_SET_NAME ioctls") Reported-by: syzbot+3643a18836bce555bff6@syzkaller.appspotmail.com Cc: [5.3+] Cc: Arnd Bergmann Reported-by: Charan Teja Reddy Reviewed-by: Arnd Bergmann Signed-off-by: Sumit Semwal Tested-by: Charan Teja Reddy Link: https://patchwork.freedesktop.org/patch/msgid/20200611114418.19852-1-sumit.semwal@linaro.org --- drivers/dma-buf/dma-buf.c | 54 ++++++++++++++++++++++------------------------- 1 file changed, 25 insertions(+), 29 deletions(-) (limited to 'drivers/dma-buf') diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 01ce125f8e8d..412629601ad3 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -54,37 +54,11 @@ static char *dmabuffs_dname(struct dentry *dentry, char *buffer, int buflen) dentry->d_name.name, ret > 0 ? name : ""); } -static const struct dentry_operations dma_buf_dentry_ops = { - .d_dname = dmabuffs_dname, -}; - -static struct vfsmount *dma_buf_mnt; - -static int dma_buf_fs_init_context(struct fs_context *fc) -{ - struct pseudo_fs_context *ctx; - - ctx = init_pseudo(fc, DMA_BUF_MAGIC); - if (!ctx) - return -ENOMEM; - ctx->dops = &dma_buf_dentry_ops; - return 0; -} - -static struct file_system_type dma_buf_fs_type = { - .name = "dmabuf", - .init_fs_context = dma_buf_fs_init_context, - .kill_sb = kill_anon_super, -}; - -static int dma_buf_release(struct inode *inode, struct file *file) +static void dma_buf_release(struct dentry *dentry) { struct dma_buf *dmabuf; - if (!is_dma_buf_file(file)) - return -EINVAL; - - dmabuf = file->private_data; + dmabuf = dentry->d_fsdata; BUG_ON(dmabuf->vmapping_counter); @@ -110,9 +84,32 @@ static int dma_buf_release(struct inode *inode, struct file *file) module_put(dmabuf->owner); kfree(dmabuf->name); kfree(dmabuf); +} + +static const struct dentry_operations dma_buf_dentry_ops = { + .d_dname = dmabuffs_dname, + .d_release = dma_buf_release, +}; + +static struct vfsmount *dma_buf_mnt; + +static int dma_buf_fs_init_context(struct fs_context *fc) +{ + struct pseudo_fs_context *ctx; + + ctx = init_pseudo(fc, DMA_BUF_MAGIC); + if (!ctx) + return -ENOMEM; + ctx->dops = &dma_buf_dentry_ops; return 0; } +static struct file_system_type dma_buf_fs_type = { + .name = "dmabuf", + .init_fs_context = dma_buf_fs_init_context, + .kill_sb = kill_anon_super, +}; + static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma) { struct dma_buf *dmabuf; @@ -412,7 +409,6 @@ static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file) } static const struct file_operations dma_buf_fops = { - .release = dma_buf_release, .mmap = dma_buf_mmap_internal, .llseek = dma_buf_llseek, .poll = dma_buf_poll, -- cgit v1.2.3 From 6348dd291e3653534a9e28e6917569bc9967b35b Mon Sep 17 00:00:00 2001 From: Charan Teja Kalla Date: Fri, 19 Jun 2020 17:27:19 +0530 Subject: dmabuf: use spinlock to access dmabuf->name MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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+] 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 --- drivers/dma-buf/dma-buf.c | 11 +++++++---- include/linux/dma-buf.h | 1 + 2 files changed, 8 insertions(+), 4 deletions(-) (limited to 'drivers/dma-buf') diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 412629601ad3..1ca609f66fdf 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 : ""); @@ -338,8 +338,10 @@ 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); @@ -402,10 +404,10 @@ 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 = { @@ -542,6 +544,7 @@ 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 ab0c156abee6..a2ca294eaebe 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; /* spinlock to protect name access */ struct module *owner; struct list_head list_node; void *priv; -- cgit v1.2.3