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libbpf: Fix invalid write loop logic in bpf_linker__add_buf()

Fix bpf_linker__add_buf()'s logic of copying data from memory buffer into
memfd. In the event of short write not writing entire buf_sz bytes into memfd
file, we'll append bytes from the beginning of buf *again* (corrupting ELF
file contents) instead of correctly appending the rest of not-yet-read buf
contents.

Closes: https://github.com/libbpf/libbpf/issues/945
Fixes: 6d5e5e5d7ce1 ("libbpf: Extend linker API to support in-memory ELF files")
Signed-off-by: Amery Hung <ameryhung@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/20260209230134.3530521-1-ameryhung@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

authored by

Amery Hung and committed by
Alexei Starovoitov 04999b99 728ff167

+1 -1
+1 -1
tools/lib/bpf/linker.c
··· 581 581 582 582 written = 0; 583 583 while (written < buf_sz) { 584 - ret = write(fd, buf, buf_sz); 584 + ret = write(fd, buf + written, buf_sz - written); 585 585 if (ret < 0) { 586 586 ret = -errno; 587 587 pr_warn("failed to write '%s': %s\n", filename, errstr(ret));