omapfb_mmap() has a race condition with OMAPFB_SETUP_PLANE ioctl that can lead to use-after-free:
The fb_mmap() entry point holds mm_lock but not lock (fb_info->lock), while ioctl handlers like OMAPFB_SETUP_PLANE hold lock but not mm_lock. This allows concurrent execution. In omapfb_mmap(): 1. rg = omapfb_get_mem_region(ofbi->region); // Get old region ref 2. start = omapfb_get_region_paddr(ofbi); // Read from NEW region 3. len = fix->smem_len; // Read from NEW region 4. vm_iomap_memory(vma, start, len); // Map NEW region memory 5. atomic_inc(&rg->map_count); // Increment OLD region! Concurrently, OMAPFB_SETUP_PLANE can: - Reassign ofbi->region = new_rg - Update fix->smem_len - OMAPFB_SETUP_MEM then checks NEW region's map_count (0!) and frees it This leaves userspace with a mapping to freed physical memory. The fix is to read all required values (start, len) from the same region reference (rg) that will have its map_count incremented, preventing the region from being freed while still mapped. Cc: [email protected] Signed-off-by: Hongling Zeng <[email protected]> --- Change in V2: -Restore fix->smem_len to maintain VRFB sparse mapping. -Increment map_count before mapping to prevent use-after-free on driver unload -Add proper error handling for map_count --- drivers/video/fbdev/omap2/omapfb/omapfb-main.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/drivers/video/fbdev/omap2/omapfb/omapfb-main.c b/drivers/video/fbdev/omap2/omapfb/omapfb-main.c index d70deb6a9150..046892682fc6 100644 --- a/drivers/video/fbdev/omap2/omapfb/omapfb-main.c +++ b/drivers/video/fbdev/omap2/omapfb/omapfb-main.c @@ -1099,7 +1099,11 @@ static int omapfb_mmap(struct fb_info *fbi, struct vm_area_struct *vma) rg = omapfb_get_mem_region(ofbi->region); - start = omapfb_get_region_paddr(ofbi); + if (ofbi->rotation_type == OMAP_DSS_ROT_VRFB) + start = rg->vrfb.paddr[0]; + else + start = rg->paddr; + len = fix->smem_len; DBG("user mmap region start %lx, len %d, off %lx\n", start, len, @@ -1109,6 +1113,8 @@ static int omapfb_mmap(struct fb_info *fbi, struct vm_area_struct *vma) vma->vm_ops = &mmap_user_ops; vma->vm_private_data = rg; + atomic_inc(&rg->map_count); + r = vm_iomap_memory(vma, start, len); if (r) goto error; @@ -1121,6 +1127,7 @@ static int omapfb_mmap(struct fb_info *fbi, struct vm_area_struct *vma) return 0; error: + atomic_dec(&rg->map_count); omapfb_put_mem_region(rg); return r; -- 2.25.1
