forked from Minki/linux
9edcad53d6
Delay the check of nd_reserved2 to the actual endpoint (acpi_nfit_ctl) that uses it, as a prevention of a potential double-fetch bug. While examining the kernel source code, I found a dangerous operation that could turn into a double-fetch situation (a race condition bug) where the same userspace memory region are fetched twice into kernel with sanity checks after the first fetch while missing checks after the second fetch. In the case of _IOC_NR(ioctl_cmd) == ND_CMD_CALL: 1. The first fetch happens in line 935 copy_from_user(&pkg, p, sizeof(pkg) 2. subsequently `pkg.nd_reserved2` is asserted to be all zeroes (line 984 to 986). 3. The second fetch happens in line 1022 copy_from_user(buf, p, buf_len) 4. Given that `p` can be fully controlled in userspace, an attacker can race condition to override the header part of `p`, say, `((struct nd_cmd_pkg *)p)->nd_reserved2` to arbitrary value (say nine 0xFFFFFFFF for `nd_reserved2`) after the first fetch but before the second fetch. The changed value will be copied to `buf`. 5. There is no checks on the second fetches until the use of it in line 1034: nd_cmd_clear_to_send(nvdimm_bus, nvdimm, cmd, buf) and line 1038: nd_desc->ndctl(nd_desc, nvdimm, cmd, buf, buf_len, &cmd_rc) which means that the assumed relation, `p->nd_reserved2` are all zeroes might not hold after the second fetch. And once the control goes to these functions we lose the context to assert the assumed relation. 6. Based on my manual analysis, `p->nd_reserved2` is not used in function `nd_cmd_clear_to_send` and potential implementations of `nd_desc->ndctl` so there is no working exploit against it right now. However, this could easily turns to an exploitable one if careless developers start to use `p->nd_reserved2` later and assume that they are all zeroes. Move the validation of the nd_reserved2 field to the ->ndctl() implementation where it has a stable buffer to evaluate. Signed-off-by: Meng Xu <mengxu.gatech@gmail.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com> |
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| .. | ||
| core.c | ||
| Kconfig | ||
| Makefile | ||
| mce.c | ||
| nfit.h | ||