On 6/2/26 10:54, Hongling Zeng wrote:
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;
In the code there is another atomic_inc() here....
With your patch, map_count is incremented twice.
Is this right?
Helge
