{"id":"CVE-2026-89996","state":"PUBLISHED","title":"dma-buf: dma-heap: don't publish fd before copy_to_user() succeeds","description":"In the Linux kernel, the following vulnerability has been resolved:\n\ndma-buf: dma-heap: don't publish fd before copy_to_user() succeeds\n\nDMA_HEAP_IOCTL_ALLOC allocates a dma-buf and installs an fd into the\ncaller's fd table via dma_buf_fd() -> fd_install() before\ndma_heap_ioctl() copies the result back to userspace.  If the trailing\ncopy_to_user() fails, userspace never learns the fd number, but the\nfd (and the underlying dma-buf reference) are already visible to\nother threads in the same process and are leaked for the lifetime of\nthe process.\n\nThe obvious \"close it on the failure path\" fix is unsafe: once\nfd_install() has run, another thread can already dup() the fd, send\nit via SCM_RIGHTS, or close() it and let its number be reused, so a\nsubsequent close_fd() from the ioctl path can operate on an unrelated\nfile.  This was pointed out by Christian König on v1 [1].\n\nRestructure the allocation path so that fd_install() is the last,\nunfailable step of a successful ioctl:\n\n  1. heap->ops->allocate()      creates the dma_buf.\n  2. get_unused_fd_flags()      reserves an fd number in the caller's\n                                fd table without publishing it, so\n                                no other thread can observe it.\n  3. copy_to_user()             delivers the fd number to userspace;\n                                on failure the fd is returned with\n                                put_unused_fd() and the dma_buf\n                                reference is dropped with\n                                dma_buf_put(), leaving no user-\n                                visible state behind.\n  4. dma_buf_fd_install()       publishes the fd and emits the\n                                trace_dma_buf_fd tracepoint -- from\n                                here on the ioctl cannot fail.\n\nA new dma_buf_fd_install() helper is introduced in dma-buf.c to wrap\nfd_install() together with the DMA_BUF_TRACE() call, preserving the\nexport tracing that dma_buf_fd() provides.  dma_heap_ioctl_allocate()\nis refactored to return the struct dma_buf * directly (returning\nERR_PTR on failure) so the caller holds the dmabuf reference across\nsteps 3 and 4.\n\nThe failure at step 3 is easily reachable from userspace: pass a\nstruct dma_heap_allocation_data that lives in a page whose protection\nis flipped to PROT_READ between copy_from_user() and copy_to_user()\n(e.g. via mprotect()).  Before this change each such ioctl leaks one\ndmabuf fd; after it, the fd table is unchanged on failure and only\n/dev/dma_heap/<name> remains open.\n\nNo UAPI or heap-driver interface change.\n\n[1] https://lore.kernel.org/dri-devel/175e98de-f414-47d7-81c1-c0fe0a8f7f62@amd.com/","publishedAt":"2026-09-16T10:33:08.620Z","updatedAt":"2026-10-30T12:33:45.249Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"c02a81fba74fe3488ad6b08bfb5a1329005418f8","status":"affected","lessThan":"1953ef8d11eb5870fe621259708a90900bead272","versionType":"git"},{"version":"c02a81fba74fe3488ad6b08bfb5a1329005418f8","status":"affected","lessThan":"ad61defb3e66ac0c598ad6f39b57f15784543d46","versionType":"git"},{"version":"c02a81fba74fe3488ad6b08bfb5a1329005418f8","status":"affected","lessThan":"1bf6083a41f810d760c4dcd1b80c5194a92575aa","versionType":"git"},{"version":"c02a81fba74fe3488ad6b08bfb5a1329005418f8","status":"affected","lessThan":"69d57dbadb27ffd5eef34fd184bab145500cdabc","versionType":"git"},{"version":"c02a81fba74fe3488ad6b08bfb5a1329005418f8","status":"affected","lessThan":"0d4a5d218055db29b50cc07d3d73d27007c2a391","versionType":"git"},{"version":"c02a81fba74fe3488ad6b08bfb5a1329005418f8","status":"affected","lessThan":"30d0aff2c65a277135cfd8ea28fa1ee75e0ea4e0","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/dma-buf/dma-buf.c","drivers/dma-buf/dma-heap.c","include/linux/dma-buf.h"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.6","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.6","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.112","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.52","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.5","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/dma-buf/dma-buf.c","drivers/dma-buf/dma-heap.c","include/linux/dma-buf.h"]}],"references":["https://git.kernel.org/stable/c/1953ef8d11eb5870fe621259708a90900bead272","https://git.kernel.org/stable/c/ad61defb3e66ac0c598ad6f39b57f15784543d46","https://git.kernel.org/stable/c/1bf6083a41f810d760c4dcd1b80c5194a92575aa","https://git.kernel.org/stable/c/69d57dbadb27ffd5eef34fd184bab145500cdabc","https://git.kernel.org/stable/c/0d4a5d218055db29b50cc07d3d73d27007c2a391","https://git.kernel.org/stable/c/30d0aff2c65a277135cfd8ea28fa1ee75e0ea4e0"],"weaknesses":[],"ingestedAt":"2026-10-30T12:52:04.348Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/89xxx/CVE-2026-89996.json","commit":"1f312381e38164a43607eebab851b151dd16861e","baselineCommit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-89996","state":"PUBLISHED","datePublished":"2026-09-16T10:33:08.620Z","dateUpdated":"2026-10-30T12:33:45.249Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-11T19:38:34.780Z"},"containers":{"cna":{"title":"dma-buf: dma-heap: don't publish fd before copy_to_user() succeeds","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\ndma-buf: dma-heap: don't publish fd before copy_to_user() succeeds\n\nDMA_HEAP_IOCTL_ALLOC allocates a dma-buf and installs an fd into the\ncaller's fd table via dma_buf_fd() -> fd_install() before\ndma_heap_ioctl() copies the result back to userspace.  If the trailing\ncopy_to_user() fails, userspace never learns the fd number, but the\nfd (and the underlying dma-buf reference) are already visible to\nother threads in the same process and are leaked for the lifetime of\nthe process.\n\nThe obvious \"close it on the failure path\" fix is unsafe: once\nfd_install() has run, another thread can already dup() the fd, send\nit via SCM_RIGHTS, or close() it and let its number be reused, so a\nsubsequent close_fd() from the ioctl path can operate on an unrelated\nfile.  This was pointed out by Christian König on v1 [1].\n\nRestructure the allocation path so that fd_install() is the last,\nunfailable step of a successful ioctl:\n\n  1. heap->ops->allocate()      creates the dma_buf.\n  2. get_unused_fd_flags()      reserves an fd number in the caller's\n                                fd table without publishing it, so\n                                no other thread can observe it.\n  3. copy_to_user()             delivers the fd number to userspace;\n                                on failure the fd is returned with\n                                put_unused_fd() and the dma_buf\n                                reference is dropped with\n                                dma_buf_put(), leaving no user-\n                                visible state behind.\n  4. dma_buf_fd_install()       publishes the fd and emits the\n                                trace_dma_buf_fd tracepoint -- from\n                                here on the ioctl cannot fail.\n\nA new dma_buf_fd_install() helper is introduced in dma-buf.c to wrap\nfd_install() together with the DMA_BUF_TRACE() call, preserving the\nexport tracing that dma_buf_fd() provides.  dma_heap_ioctl_allocate()\nis refactored to return the struct dma_buf * directly (returning\nERR_PTR on failure) so the caller holds the dmabuf reference across\nsteps 3 and 4.\n\nThe failure at step 3 is easily reachable from userspace: pass a\nstruct dma_heap_allocation_data that lives in a page whose protection\nis flipped to PROT_READ between copy_from_user() and copy_to_user()\n(e.g. via mprotect()).  Before this change each such ioctl leaks one\ndmabuf fd; after it, the fd table is unchanged on failure and only\n/dev/dma_heap/<name> remains open.\n\nNo UAPI or heap-driver interface change.\n\n[1] https://lore.kernel.org/dri-devel/175e98de-f414-47d7-81c1-c0fe0a8f7f62@amd.com/"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"c02a81fba74fe3488ad6b08bfb5a1329005418f8","status":"affected","lessThan":"1953ef8d11eb5870fe621259708a90900bead272","versionType":"git"},{"version":"c02a81fba74fe3488ad6b08bfb5a1329005418f8","status":"affected","lessThan":"ad61defb3e66ac0c598ad6f39b57f15784543d46","versionType":"git"},{"version":"c02a81fba74fe3488ad6b08bfb5a1329005418f8","status":"affected","lessThan":"1bf6083a41f810d760c4dcd1b80c5194a92575aa","versionType":"git"},{"version":"c02a81fba74fe3488ad6b08bfb5a1329005418f8","status":"affected","lessThan":"69d57dbadb27ffd5eef34fd184bab145500cdabc","versionType":"git"},{"version":"c02a81fba74fe3488ad6b08bfb5a1329005418f8","status":"affected","lessThan":"0d4a5d218055db29b50cc07d3d73d27007c2a391","versionType":"git"},{"version":"c02a81fba74fe3488ad6b08bfb5a1329005418f8","status":"affected","lessThan":"30d0aff2c65a277135cfd8ea28fa1ee75e0ea4e0","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/dma-buf/dma-buf.c","drivers/dma-buf/dma-heap.c","include/linux/dma-buf.h"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.6","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.6","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.160","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.112","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.52","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.5","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["drivers/dma-buf/dma-buf.c","drivers/dma-buf/dma-heap.c","include/linux/dma-buf.h"]}],"references":[{"url":"https://git.kernel.org/stable/c/1953ef8d11eb5870fe621259708a90900bead272"},{"url":"https://git.kernel.org/stable/c/ad61defb3e66ac0c598ad6f39b57f15784543d46"},{"url":"https://git.kernel.org/stable/c/1bf6083a41f810d760c4dcd1b80c5194a92575aa"},{"url":"https://git.kernel.org/stable/c/69d57dbadb27ffd5eef34fd184bab145500cdabc"},{"url":"https://git.kernel.org/stable/c/0d4a5d218055db29b50cc07d3d73d27007c2a391"},{"url":"https://git.kernel.org/stable/c/30d0aff2c65a277135cfd8ea28fa1ee75e0ea4e0"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-30T12:33:45.249Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.6","versionEndExcluding":"6.1.191"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.6","versionEndExcluding":"6.6.160"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.6","versionEndExcluding":"6.12.112"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.6","versionEndExcluding":"6.18.52"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.6","versionEndExcluding":"7.2.5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.6","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}