The branch main has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=7893a7edb43e7c7328f8f46e3929e2412b45d048
commit 7893a7edb43e7c7328f8f46e3929e2412b45d048 Author: Mark Johnston <[email protected]> AuthorDate: 2026-07-27 15:42:49 +0000 Commit: Mark Johnston <[email protected]> CommitDate: 2026-07-29 17:45:02 +0000 coredump: Don't assume that the number of ELF segments is consistent In an ELF coredump, each dumped vm_map_entry is represented by a segment. __elfN(coredump) first computes the number of segments by looping over the vm_map entries (in each_dumpable_segment()), then allocates a buffer to hold the ELF header and program headers, then loops over the entries again to populate the program headers. each_dumpable_segment() holds the vm_map read lock, but that lock is dropped between the two calls. If the map is shared with another process, via rfork(), then the map can change. cb_put_phdr() did not account for this, and so could write out of bounds. Add a check to prevent this; simply do not write out excess segments. Approved by: so Security: FreeBSD-SA-26:55.elf Security: CVE-2026-58088 Reported by: Maik Muench of Secfault Security Reviewed by: kib, emaste Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D58416 --- sys/kern/imgact_elf.c | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-) diff --git a/sys/kern/imgact_elf.c b/sys/kern/imgact_elf.c index 7c78d66b3648..08e9718c4d24 100644 --- a/sys/kern/imgact_elf.c +++ b/sys/kern/imgact_elf.c @@ -1585,6 +1585,8 @@ typedef void (*segment_callback)(vm_map_entry_t, void *); struct phdr_closure { Elf_Phdr *phdr; /* Program header to fill in */ Elf_Off offset; /* Offset of segment in core file */ + int numsegs; /* Maximum number of segments */ + int nextseg; /* Next segment to fill in */ }; struct note_info { @@ -1701,10 +1703,15 @@ __elfN(coredump)(struct thread *td, struct coredump_writer *cdw, off_t limit, in } /* - * Allocate memory for building the header, fill it up, - * and write it out following the notes. + * Allocate memory for building the header, fill it up, and write it out + * following the notes. + * + * Note that a process sharing our vmspace might be concurrently + * mutating the map, in which case we could populate fewer than + * seginfo.count headers. Zero the buffer to ensure that unpopulated + * headers are still initialized. */ - hdr = malloc(hdrsize, M_TEMP, M_WAITOK); + hdr = malloc(hdrsize, M_TEMP, M_WAITOK | M_ZERO); error = __elfN(corehdr)(¶ms, seginfo.count, hdr, hdrsize, ¬elst, notesz, flags); @@ -1757,6 +1764,11 @@ cb_put_phdr(vm_map_entry_t entry, void *closure) struct phdr_closure *phc = (struct phdr_closure *)closure; Elf_Phdr *phdr = phc->phdr; + if (phc->nextseg >= phc->numsegs) { + /* Only write as many headers as we have space for. */ + return; + } + phc->offset = round_page(phc->offset); phdr->p_type = PT_LOAD; @@ -1769,6 +1781,8 @@ cb_put_phdr(vm_map_entry_t entry, void *closure) phc->offset += phdr->p_filesz; phc->phdr++; + + phc->nextseg++; } /* @@ -2031,6 +2045,8 @@ __elfN(puthdr)(struct thread *td, void *hdr, size_t hdrsize, int numsegs, /* All the writable segments from the program. */ phc.phdr = phdr; phc.offset = round_page(hdrsize + notesz); + phc.numsegs = numsegs; + phc.nextseg = 0; each_dumpable_segment(td, cb_put_phdr, &phc, flags); }
