59 lines
No EOL
2.4 KiB
Text
59 lines
No EOL
2.4 KiB
Text
Source: https://code.google.com/p/google-security-research/issues/detail?id=492
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The Samsung Graphics 2D driver (/dev/fimg2d) is accessible by unprivileged users/applications. It was found that the ioctl implementation for this driver contains a locking error which can lead to memory errors (such as use-after-free) due to a race condition.
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The key observation is in the locking routine definitions in fimg2d.h:
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#ifdef BLIT_WORKQUE
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#define g2d_lock(x) do {} while (0)
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#define g2d_unlock(x) do {} while (0)
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#define g2d_spin_lock(x, f) spin_lock_irqsave(x, f)
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#define g2d_spin_unlock(x, f) spin_unlock_irqrestore(x, f)
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#else
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#define g2d_lock(x) mutex_lock(x)
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#define g2d_unlock(x) mutex_unlock(x)
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#define g2d_spin_lock(x, f) do { f = 0; } while (0)
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#define g2d_spin_unlock(x, f) do { f = 0; } while (0)
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#endif
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This means that the g2d_lock/g2d_unlock routines are no-ops when BLIT_WORKQUE is defined, which appears to be the default configuration. Unfortunately the alternative spin lock routines are not used consistently with this configuration. For example, the FIMG2D_BITBLT_BLIT ioctl command (with notes annotated as "PZ"):
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ctx = file->private_data; /* PZ: ctx allocated at open(), lives on the heap. */
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switch (cmd) {
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case FIMG2D_BITBLT_BLIT:
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mm = get_task_mm(current);
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if (!mm) {
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fimg2d_err("no mm for ctx\n");
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return -ENXIO;
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}
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g2d_lock(&ctrl->drvlock); /* PZ: This is a no-op. */
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ctx->mm = mm;
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ret = fimg2d_add_command(ctrl, ctx, (struct fimg2d_blit __user *)arg);
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if (ret) {
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...
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}
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ret = fimg2d_request_bitblt(ctrl, ctx); /* PZ: Does stuff with the ctx. */
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if (ret) {
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...
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}
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g2d_unlock(&ctrl->drvlock); /* PZ: Another no-op */
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As the lock macros are no-ops, a second process can change ctx->mm when the original process is still using the same ctx->mm (as long as it has access to the same file descriptor).
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Reproduction steps:
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Open /dev/fimg2d
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Fork to get two processes with different mm’s with the access to the fd
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Concurrently call the FIMG2D_BITBLT_BLIT ioctl from both processes.
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One ioctl should have valid data, the other should fail
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At this point ctx->mm will now have invalid or free data (free if the forked process dies). Proof-of-concept code to trigger this condition is attached (fimg2d-lock.c)
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Proof of Concept:
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https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/38557.zip |