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privsep: Ensure we recv for real after a successful recv MSG_PEEK #556

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privsep: Ensure we recv for real after a successful recv MSG_PEEK #556

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privsep: Ensure we recv for real after a successful recv MSG_PEEK
rsmarples Nov 17, 2025
834a322
Improve commentary for prior
rsmarples Nov 18, 2025
595c305
More minor comments.
rsmarples Nov 18, 2025
36d3dad
Return EBADMSG on recvmsg len mismatch
rsmarples Nov 30, 2025
a3ce698
Improve comments.
rsmarples Nov 30, 2025
cd75b08
Don't work out buffers on a truncated header.
rsmarples Nov 30, 2025
16a0bfb
Move the vars for reading onto the stack and off the context
rsmarples Dec 3, 2025
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32 changes: 18 additions & 14 deletions src/privsep-root.c
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Original file line number Diff line number Diff line change
Expand Up @@ -86,6 +86,7 @@ ps_root_readerrorcb(struct psr_ctx *psr_ctx)
{ .iov_base = psr_error, .iov_len = sizeof(*psr_error) },
{ .iov_base = NULL, .iov_len = 0 },
};
struct msghdr msg = { .msg_iov = iov, .msg_iovlen = __arraycount(iov) };
ssize_t len;

#define PSR_ERROR(e) \
Expand All @@ -98,37 +99,40 @@ ps_root_readerrorcb(struct psr_ctx *psr_ctx)
if (eloop_waitfd(fd) == -1)
PSR_ERROR(errno);

len = recv(fd, psr_error, sizeof(*psr_error), MSG_PEEK);
len = recvmsg(fd, &msg, MSG_PEEK | MSG_WAITALL);
if (len == -1)
PSR_ERROR(errno);
else if ((size_t)len < sizeof(*psr_error))
PSR_ERROR(EINVAL);
goto recv;

if (psr_error->psr_datalen > SSIZE_MAX)
PSR_ERROR(ENOBUFS);
if (psr_ctx->psr_usemdata &&
psr_error->psr_datalen > psr_ctx->psr_mdatalen)
{
void *d = realloc(psr_ctx->psr_mdata, psr_error->psr_datalen);
if (d == NULL)
PSR_ERROR(errno);
psr_ctx->psr_mdata = d;
psr_ctx->psr_mdatalen = psr_error->psr_datalen;

if (d != NULL) {
psr_ctx->psr_mdata = d;
psr_ctx->psr_mdatalen = psr_error->psr_datalen;
}
}
if (psr_error->psr_datalen != 0) {
if (psr_ctx->psr_usemdata)
if (psr_ctx->psr_usemdata) {
iov[1].iov_base = psr_ctx->psr_mdata;
else {
if (psr_error->psr_datalen > psr_ctx->psr_datalen)
PSR_ERROR(ENOBUFS);
iov[1].iov_len = psr_ctx->psr_mdatalen;
} else {
iov[1].iov_base = psr_ctx->psr_data;
iov[1].iov_len = psr_ctx->psr_datalen;
}
iov[1].iov_len = psr_error->psr_datalen;
}

len = readv(fd, iov, __arraycount(iov));
recv:
len = recvmsg(fd, &msg, MSG_WAITALL);
if (len == -1)
PSR_ERROR(errno);
else if ((size_t)len < sizeof(*psr_error))
PSR_ERROR(EINVAL);
else if (msg.msg_flags & MSG_TRUNC)
PSR_ERROR(ENOBUFS);
else if ((size_t)len != sizeof(*psr_error) + psr_error->psr_datalen)
PSR_ERROR(EINVAL);
return len;
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